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 $96.37   11.584%   $107.5335   $107.53   $107.55   $107.50  
  Purchase #2 $58.49   11.396%   $65.1555   $65.16   $65.15   $65.20  
  Purchase #3 $65.56   3.676%   $67.97   $67.97   $67.95   $68.00  
  Purchase #4 $158.39   5.203%   $166.631   $166.63   $166.65   $166.60  
  Purchase #5 $90.54   13.490%   $102.7538   $102.75   $102.75   $102.80  
  Purchase #6 $156.58   8.478%   $169.8549   $169.85   $169.85   $169.90  
  Purchase #7 $232.68   6.509%   $247.8251   $247.83   $247.85   $247.80  
  7 purchase totals = $858.61       $927.7238   $927.72   $927.75   $927.80