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 $143.51   5.637%   $151.5997   $151.60   $151.60   $151.60  
  Purchase #2 $201.62   12.251%   $226.3205   $226.32   $226.30   $226.30  
  Purchase #3 $75.84   11.549%   $84.5988   $84.60   $84.60   $84.60  
  Purchase #4 $34.44   3.634%   $35.6915   $35.69   $35.70   $35.70  
  Purchase #5 $246.78   3.701%   $255.9133   $255.91   $255.90   $255.90  
  Purchase #6 $53.53   3.643%   $55.4801   $55.48   $55.50   $55.50  
  Purchase #7 $94.53   4.873%   $99.1364   $99.14   $99.15   $99.10  
  7 purchase totals = $850.25       $908.7403   $908.74   $908.75   $908.70