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 $85.87   6.618%   $91.5529   $91.55   $91.55   $91.60  
  Purchase #2 $247.40   8.564%   $268.5873   $268.59   $268.60   $268.60  
  Purchase #3 $58.90   10.825%   $65.2759   $65.28   $65.30   $65.30  
  Purchase #4 $117.65   6.503%   $125.3008   $125.30   $125.30   $125.30  
  Purchase #5 $88.58   6.290%   $94.1517   $94.15   $94.15   $94.20  
  Purchase #6 $167.89   7.645%   $180.7252   $180.73   $180.75   $180.70  
  Purchase #7 $6.95   5.393%   $7.3248   $7.32   $7.30   $7.30  
  7 purchase totals = $773.24       $832.9186   $832.92   $832.95   $833.00