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 $58.67   11.781%   $65.5819   $65.58   $65.60   $65.60  
  Purchase #2 $220.84   7.254%   $236.8597   $236.86   $236.85   $236.90  
  Purchase #3 $23.94   7.570%   $25.7523   $25.75   $25.75   $25.80  
  Purchase #4 $84.63   12.487%   $95.1977   $95.20   $95.20   $95.20  
  Purchase #5 $148.73   12.737%   $167.6737   $167.67   $167.65   $167.70  
  Purchase #6 $81.96   12.589%   $92.2779   $92.28   $92.30   $92.30  
  Purchase #7 $203.42   10.132%   $224.0305   $224.03   $224.05   $224.00  
  7 purchase totals = $822.19       $907.3737   $907.37   $907.40   $907.50