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 $112.81   11.142%   $125.3793   $125.38   $125.40   $125.40  
  Purchase #2 $73.64   6.403%   $78.3552   $78.36   $78.35   $78.40  
  Purchase #3 $235.80   4.831%   $247.1915   $247.19   $247.20   $247.20  
  Purchase #4 $98.55   6.278%   $104.737   $104.74   $104.75   $104.70  
  Purchase #5 $58.85   13.650%   $66.883   $66.88   $66.90   $66.90  
  Purchase #6 $187.53   6.107%   $198.9825   $198.98   $199.00   $199.00  
  Purchase #7 $208.31   4.627%   $217.9485   $217.95   $217.95   $217.90  
  7 purchase totals = $975.49       $1,039.4770   $1,039.48   $1,039.55   $1,039.50