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 $61.33   8.357%   $66.4553   $66.46   $66.45   $66.50  
  Purchase #2 $77.39   4.497%   $80.8702   $80.87   $80.85   $80.90  
  Purchase #3 $191.41   8.655%   $207.9765   $207.98   $208.00   $208.00  
  Purchase #4 $220.73   8.550%   $239.6024   $239.60   $239.60   $239.60  
  Purchase #5 $205.41   10.218%   $226.3988   $226.40   $226.40   $226.40  
  Purchase #6 $80.34   9.865%   $88.2655   $88.27   $88.25   $88.30  
  Purchase #7 $42.55   11.473%   $47.4318   $47.43   $47.45   $47.40  
  7 purchase totals = $879.16       $957.0005   $957.01   $957.00   $957.10