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 $240.57   7.534%   $258.6945   $258.69   $258.70   $258.70  
  Purchase #2 $101.82   8.175%   $110.1438   $110.14   $110.15   $110.10  
  Purchase #3 $149.44   10.200%   $164.6829   $164.68   $164.70   $164.70  
  Purchase #4 $156.33   7.176%   $167.5482   $167.55   $167.55   $167.50  
  Purchase #5 $41.27   8.858%   $44.9257   $44.93   $44.95   $44.90  
  Purchase #6 $118.56   11.356%   $132.0237   $132.02   $132.00   $132.00  
  Purchase #7 $5.94   13.163%   $6.7219   $6.72   $6.70   $6.70  
  7 purchase totals = $813.93       $884.7407   $884.73   $884.75   $884.60