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 $206.69   6.662%   $220.4597   $220.46   $220.45   $220.50  
  Purchase #2 $131.90   10.852%   $146.2138   $146.21   $146.20   $146.20  
  Purchase #3 $98.36   6.367%   $104.6226   $104.62   $104.60   $104.60  
  Purchase #4 $57.34   7.192%   $61.4639   $61.46   $61.45   $61.50  
  Purchase #5 $212.38   13.190%   $240.3929   $240.39   $240.40   $240.40  
  Purchase #6 $108.64   9.184%   $118.6175   $118.62   $118.60   $118.60  
  Purchase #7 $158.42   11.225%   $176.2026   $176.20   $176.20   $176.20  
  7 purchase totals = $973.73       $1,067.9730   $1,067.96   $1,067.90   $1,068.00