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 $23.46   3.107%   $24.1889   $24.19   $24.20   $24.20  
  Purchase #2 $221.95   3.444%   $229.594   $229.59   $229.60   $229.60  
  Purchase #3 $183.60   10.378%   $202.654   $202.65   $202.65   $202.70  
  Purchase #4 $211.89   3.629%   $219.5795   $219.58   $219.60   $219.60  
  Purchase #5 $128.86   10.586%   $142.5011   $142.50   $142.50   $142.50  
  Purchase #6 $169.50   4.609%   $177.3123   $177.31   $177.30   $177.30  
  Purchase #7 $22.58   12.499%   $25.4023   $25.40   $25.40   $25.40  
  7 purchase totals = $961.84       $1,021.2321   $1,021.22   $1,021.25   $1,021.30