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 $151.42   6.342%   $161.0231   $161.02   $161.00   $161.00  
  Purchase #2 $175.60   13.852%   $199.9241   $199.92   $199.90   $199.90  
  Purchase #3 $53.46   11.766%   $59.7501   $59.75   $59.75   $59.80  
  Purchase #4 $225.50   5.833%   $238.6534   $238.65   $238.65   $238.70  
  Purchase #5 $107.70   10.142%   $118.6229   $118.62   $118.60   $118.60  
  Purchase #6 $217.42   5.201%   $228.728   $228.73   $228.75   $228.70  
  Purchase #7 $164.45   3.848%   $170.778   $170.78   $170.80   $170.80  
  7 purchase totals = $1,095.55       $1,177.4796   $1,177.47   $1,177.45   $1,177.50