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 $108.61   10.180%   $119.6665   $119.67   $119.65   $119.70  
  Purchase #2 $237.30   8.583%   $257.6675   $257.67   $257.65   $257.70  
  Purchase #3 $136.61   10.121%   $150.4363   $150.44   $150.45   $150.40  
  Purchase #4 $238.88   3.293%   $246.7463   $246.75   $246.75   $246.70  
  Purchase #5 $105.49   4.472%   $110.2075   $110.21   $110.20   $110.20  
  Purchase #6 $232.43   11.859%   $259.9939   $259.99   $260.00   $260.00  
  Purchase #7 $124.49   3.781%   $129.197   $129.20   $129.20   $129.20  
  7 purchase totals = $1,183.81       $1,273.9150   $1,273.93   $1,273.90   $1,273.90