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 $37.83   9.652%   $41.4814   $41.48   $41.50   $41.50  
  Purchase #2 $226.39   11.809%   $253.1244   $253.12   $253.10   $253.10  
  Purchase #3 $56.31   4.123%   $58.6317   $58.63   $58.65   $58.60  
  Purchase #4 $94.45   4.242%   $98.4566   $98.46   $98.45   $98.50  
  Purchase #5 $195.85   3.181%   $202.08   $202.08   $202.10   $202.10  
  Purchase #6 $243.87   6.853%   $260.5824   $260.58   $260.60   $260.60  
  Purchase #7 $27.90   12.168%   $31.2949   $31.29   $31.30   $31.30  
  7 purchase totals = $882.60       $945.6514   $945.64   $945.70   $945.70