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 $58.76   3.779%   $60.9805   $60.98   $61.00   $61.00  
  Purchase #2 $188.49   3.319%   $194.746   $194.75   $194.75   $194.70  
  Purchase #3 $42.66   11.828%   $47.7058   $47.71   $47.70   $47.70  
  Purchase #4 $207.71   9.361%   $227.1537   $227.15   $227.15   $227.20  
  Purchase #5 $160.91   8.686%   $174.8866   $174.89   $174.90   $174.90  
  Purchase #6 $102.53   10.618%   $113.4166   $113.42   $113.40   $113.40  
  Purchase #7 $180.60   5.202%   $189.9948   $189.99   $190.00   $190.00  
  7 purchase totals = $941.66       $1,008.8840   $1,008.89   $1,008.90   $1,008.90