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 $104.47   11.756%   $116.7515   $116.75   $116.75   $116.80  
  Purchase #2 $208.36   4.169%   $217.0465   $217.05   $217.05   $217.00  
  Purchase #3 $11.37   3.603%   $11.7797   $11.78   $11.80   $11.80  
  Purchase #4 $190.56   6.331%   $202.6244   $202.62   $202.60   $202.60  
  Purchase #5 $35.30   6.826%   $37.7096   $37.71   $37.70   $37.70  
  Purchase #6 $240.46   11.142%   $267.2521   $267.25   $267.25   $267.30  
  Purchase #7 $52.26   12.294%   $58.6848   $58.68   $58.70   $58.70  
  7 purchase totals = $842.78       $911.8486   $911.84   $911.85   $911.90