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 $83.30   11.354%   $92.7579   $92.76   $92.75   $92.80  
  Purchase #2 $77.65   8.207%   $84.0227   $84.02   $84.00   $84.00  
  Purchase #3 $167.81   9.228%   $183.2955   $183.30   $183.30   $183.30  
  Purchase #4 $214.78   8.357%   $232.7292   $232.73   $232.75   $232.70  
  Purchase #5 $214.76   6.417%   $228.5411   $228.54   $228.55   $228.50  
  Purchase #6 $45.65   5.602%   $48.2073   $48.21   $48.20   $48.20  
  Purchase #7 $152.97   8.679%   $166.2463   $166.25   $166.25   $166.20  
  7 purchase totals = $956.92       $1,035.8000   $1,035.81   $1,035.80   $1,035.70