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 $97.49   8.286%   $105.568   $105.57   $105.55   $105.60  
  Purchase #2 $115.93   3.169%   $119.6038   $119.60   $119.60   $119.60  
  Purchase #3 $60.32   13.300%   $68.3426   $68.34   $68.35   $68.30  
  Purchase #4 $93.65   11.487%   $104.4076   $104.41   $104.40   $104.40  
  Purchase #5 $99.27   5.259%   $104.4906   $104.49   $104.50   $104.50  
  Purchase #6 $13.73   13.755%   $15.6186   $15.62   $15.60   $15.60  
  Purchase #7 $234.36   5.294%   $246.767   $246.77   $246.75   $246.80  
  7 purchase totals = $714.75       $764.7982   $764.80   $764.75   $764.80