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 $181.69   6.361%   $193.2473   $193.25   $193.25   $193.20  
  Purchase #2 $200.40   12.473%   $225.3959   $225.40   $225.40   $225.40  
  Purchase #3 $65.29   7.238%   $70.0157   $70.02   $70.00   $70.00  
  Purchase #4 $55.42   6.544%   $59.0467   $59.05   $59.05   $59.00  
  Purchase #5 $34.95   12.131%   $39.1898   $39.19   $39.20   $39.20  
  Purchase #6 $92.94   12.592%   $104.643   $104.64   $104.65   $104.60  
  Purchase #7 $106.44   9.161%   $116.191   $116.19   $116.20   $116.20  
  7 purchase totals = $737.13       $807.7294   $807.74   $807.75   $807.60