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 $185.97   12.291%   $208.8276   $208.83   $208.85   $208.80  
  Purchase #2 $75.31   6.797%   $80.4288   $80.43   $80.45   $80.40  
  Purchase #3 $44.33   5.190%   $46.6307   $46.63   $46.65   $46.60  
  Purchase #4 $121.42   3.196%   $125.3006   $125.30   $125.30   $125.30  
  Purchase #5 $167.49   9.428%   $183.281   $183.28   $183.30   $183.30  
  Purchase #6 $213.92   5.799%   $226.3252   $226.33   $226.35   $226.30  
  Purchase #7 $72.97   7.661%   $78.5602   $78.56   $78.55   $78.60  
  7 purchase totals = $881.41       $949.3541   $949.36   $949.45   $949.30