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 $186.57   10.717%   $206.5647   $206.56   $206.55   $206.60  
  Purchase #2 $220.29   9.548%   $241.3233   $241.32   $241.30   $241.30  
  Purchase #3 $242.36   12.604%   $272.9071   $272.91   $272.90   $272.90  
  Purchase #4 $233.48   13.497%   $264.9928   $264.99   $265.00   $265.00  
  Purchase #5 $184.57   9.274%   $201.687   $201.69   $201.70   $201.70  
  Purchase #6 $17.59   12.242%   $19.7434   $19.74   $19.75   $19.70  
  Purchase #7 $194.44   9.120%   $212.1729   $212.17   $212.15   $212.20  
  7 purchase totals = $1,279.30       $1,419.3912   $1,419.38   $1,419.35   $1,419.40