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 $67.75   4.358%   $70.7025   $70.70   $70.70   $70.70  
  Purchase #2 $25.37   5.518%   $26.7699   $26.77   $26.75   $26.80  
  Purchase #3 $225.62   10.845%   $250.0885   $250.09   $250.10   $250.10  
  Purchase #4 $152.49   9.231%   $166.5664   $166.57   $166.55   $166.60  
  Purchase #5 $51.29   8.821%   $55.8143   $55.81   $55.80   $55.80  
  Purchase #6 $152.28   12.197%   $170.8536   $170.85   $170.85   $170.90  
  Purchase #7 $51.99   4.358%   $54.2557   $54.26   $54.25   $54.30  
  7 purchase totals = $726.79       $795.0509   $795.05   $795.00   $795.20