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 $59.76   12.222%   $67.0639   $67.06   $67.05   $67.10  
  Purchase #2 $35.39   9.579%   $38.78   $38.78   $38.80   $38.80  
  Purchase #3 $108.84   12.471%   $122.4134   $122.41   $122.40   $122.40  
  Purchase #4 $11.91   8.637%   $12.9387   $12.94   $12.95   $12.90  
  Purchase #5 $144.70   5.300%   $152.3691   $152.37   $152.35   $152.40  
  Purchase #6 $141.89   10.437%   $156.6991   $156.70   $156.70   $156.70  
  Purchase #7 $232.70   13.474%   $264.054   $264.05   $264.05   $264.10  
  7 purchase totals = $735.19       $814.3182   $814.31   $814.30   $814.40