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 $56.97   10.390%   $62.8892   $62.89   $62.90   $62.90  
  Purchase #2 $240.53   5.343%   $253.3815   $253.38   $253.40   $253.40  
  Purchase #3 $76.68   6.602%   $81.7424   $81.74   $81.75   $81.70  
  Purchase #4 $205.44   5.615%   $216.9755   $216.98   $217.00   $217.00  
  Purchase #5 $89.45   10.835%   $99.1419   $99.14   $99.15   $99.10  
  Purchase #6 $135.54   9.237%   $148.0598   $148.06   $148.05   $148.10  
  Purchase #7 $177.26   11.811%   $198.1962   $198.20   $198.20   $198.20  
  7 purchase totals = $981.87       $1,060.3865   $1,060.39   $1,060.45   $1,060.40