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 $193.70   11.495%   $215.9658   $215.97   $215.95   $216.00  
  Purchase #2 $55.88   6.706%   $59.6273   $59.63   $59.65   $59.60  
  Purchase #3 $110.33   6.766%   $117.7949   $117.79   $117.80   $117.80  
  Purchase #4 $54.60   8.283%   $59.1225   $59.12   $59.10   $59.10  
  Purchase #5 $45.66   3.681%   $47.3407   $47.34   $47.35   $47.30  
  Purchase #6 $121.54   6.813%   $129.8205   $129.82   $129.80   $129.80  
  Purchase #7 $124.40   9.119%   $135.744   $135.74   $135.75   $135.70  
  7 purchase totals = $706.11       $765.4157   $765.41   $765.40   $765.30