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 $224.87   12.835%   $253.7321   $253.73   $253.75   $253.70  
  Purchase #2 $163.57   12.755%   $184.4334   $184.43   $184.45   $184.40  
  Purchase #3 $155.47   4.139%   $161.9049   $161.90   $161.90   $161.90  
  Purchase #4 $54.39   13.383%   $61.669   $61.67   $61.65   $61.70  
  Purchase #5 $162.98   5.452%   $171.8657   $171.87   $171.85   $171.90  
  Purchase #6 $97.85   8.717%   $106.3796   $106.38   $106.40   $106.40  
  Purchase #7 $96.25   11.188%   $107.0185   $107.02   $107.00   $107.00  
  7 purchase totals = $955.38       $1,047.0032   $1,047.00   $1,047.00   $1,047.00