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 $113.87   9.411%   $124.5863   $124.59   $124.60   $124.60  
  Purchase #2 $56.39   4.427%   $58.8864   $58.89   $58.90   $58.90  
  Purchase #3 $46.94   3.489%   $48.5777   $48.58   $48.60   $48.60  
  Purchase #4 $166.68   7.463%   $179.1193   $179.12   $179.10   $179.10  
  Purchase #5 $88.46   6.389%   $94.1117   $94.11   $94.10   $94.10  
  Purchase #6 $22.28   11.241%   $24.7845   $24.78   $24.80   $24.80  
  Purchase #7 $158.61   9.689%   $173.9777   $173.98   $174.00   $174.00  
  7 purchase totals = $653.23       $704.0436   $704.05   $704.10   $704.10