Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $204.57   13.686%   $232.5675   $232.57   $232.55   $232.60  
  Purchase #2 $96.29   11.273%   $107.1448   $107.14   $107.15   $107.10  
  Purchase #3 $115.59   12.442%   $129.9717   $129.97   $129.95   $130.00  
  Purchase #4 $155.38   12.291%   $174.4778   $174.48   $174.50   $174.50  
  Purchase #5 $180.53   8.648%   $196.1422   $196.14   $196.15   $196.10  
  Purchase #6 $177.63   13.479%   $201.5727   $201.57   $201.55   $201.60  
  Purchase #7 $141.89   5.467%   $149.6471   $149.65   $149.65   $149.60  
  7 purchase totals = $1,071.88       $1,191.5238   $1,191.52   $1,191.50   $1,191.50