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 $66.30   12.567%   $74.6319   $74.63   $74.65   $74.60  
  Purchase #2 $206.46   11.266%   $229.7198   $229.72   $229.70   $229.70  
  Purchase #3 $45.88   11.799%   $51.2934   $51.29   $51.30   $51.30  
  Purchase #4 $224.53   13.593%   $255.0504   $255.05   $255.05   $255.10  
  Purchase #5 $185.44   8.574%   $201.3396   $201.34   $201.35   $201.30  
  Purchase #6 $150.29   10.283%   $165.7443   $165.74   $165.75   $165.70  
  Purchase #7 $46.49   13.321%   $52.6829   $52.68   $52.70   $52.70  
  7 purchase totals = $925.39       $1,030.4623   $1,030.45   $1,030.50   $1,030.40