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 $110.82   13.867%   $126.1874   $126.19   $126.20   $126.20  
  Purchase #2 $147.36   5.326%   $155.2084   $155.21   $155.20   $155.20  
  Purchase #3 $155.97   12.258%   $175.0888   $175.09   $175.10   $175.10  
  Purchase #4 $88.47   6.819%   $94.5028   $94.50   $94.50   $94.50  
  Purchase #5 $97.87   10.181%   $107.8341   $107.83   $107.85   $107.80  
  Purchase #6 $96.28   5.257%   $101.3414   $101.34   $101.35   $101.30  
  Purchase #7 $36.63   13.578%   $41.6036   $41.60   $41.60   $41.60  
  7 purchase totals = $733.40       $801.7665   $801.76   $801.80   $801.70