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 $116.34   6.560%   $123.9719   $123.97   $123.95   $124.00  
  Purchase #2 $28.66   13.695%   $32.585   $32.59   $32.60   $32.60  
  Purchase #3 $201.89   4.507%   $210.9892   $210.99   $211.00   $211.00  
  Purchase #4 $145.67   13.777%   $165.739   $165.74   $165.75   $165.70  
  Purchase #5 $97.99   7.189%   $105.0345   $105.03   $105.05   $105.00  
  Purchase #6 $108.48   11.783%   $121.2622   $121.26   $121.25   $121.30  
  Purchase #7 $163.73   3.415%   $169.3214   $169.32   $169.30   $169.30  
  7 purchase totals = $862.76       $928.9032   $928.90   $928.90   $928.90