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 $41.88   13.143%   $47.3843   $47.38   $47.40   $47.40  
  Purchase #2 $157.96   12.271%   $177.3433   $177.34   $177.35   $177.30  
  Purchase #3 $152.47   11.628%   $170.1992   $170.20   $170.20   $170.20  
  Purchase #4 $185.78   11.139%   $206.474   $206.47   $206.45   $206.50  
  Purchase #5 $151.80   6.360%   $161.4545   $161.45   $161.45   $161.50  
  Purchase #6 $53.26   9.474%   $58.3059   $58.31   $58.30   $58.30  
  Purchase #7 $211.87   7.562%   $227.8916   $227.89   $227.90   $227.90  
  7 purchase totals = $955.02       $1,049.0528   $1,049.04   $1,049.05   $1,049.10