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 $180.76   13.864%   $205.8206   $205.82   $205.80   $205.80  
  Purchase #2 $9.38   4.465%   $9.7988   $9.80   $9.80   $9.80  
  Purchase #3 $136.40   9.442%   $149.2789   $149.28   $149.30   $149.30  
  Purchase #4 $193.71   8.696%   $210.555   $210.56   $210.55   $210.60  
  Purchase #5 $128.92   13.516%   $146.3448   $146.34   $146.35   $146.30  
  Purchase #6 $99.91   3.308%   $103.215   $103.22   $103.20   $103.20  
  Purchase #7 $199.33   4.595%   $208.4892   $208.49   $208.50   $208.50  
  7 purchase totals = $948.41       $1,033.5023   $1,033.51   $1,033.50   $1,033.50