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 $133.79   9.555%   $146.5736   $146.57   $146.55   $146.60  
  Purchase #2 $210.60   10.516%   $232.7467   $232.75   $232.75   $232.70  
  Purchase #3 $248.37   12.640%   $279.764   $279.76   $279.75   $279.80  
  Purchase #4 $5.61   9.752%   $6.1571   $6.16   $6.15   $6.20  
  Purchase #5 $66.84   13.852%   $76.0987   $76.10   $76.10   $76.10  
  Purchase #6 $113.38   9.383%   $124.0184   $124.02   $124.00   $124.00  
  Purchase #7 $116.68   9.326%   $127.5616   $127.56   $127.55   $127.60  
  7 purchase totals = $895.27       $992.9201   $992.92   $992.85   $993.00