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 $231.25   10.553%   $255.6538   $255.65   $255.65   $255.70  
  Purchase #2 $211.75   5.279%   $222.9283   $222.93   $222.95   $222.90  
  Purchase #3 $218.33   12.319%   $245.2261   $245.23   $245.25   $245.20  
  Purchase #4 $62.43   11.792%   $69.7917   $69.79   $69.80   $69.80  
  Purchase #5 $46.47   7.819%   $50.1035   $50.10   $50.10   $50.10  
  Purchase #6 $180.38   8.264%   $195.2866   $195.29   $195.30   $195.30  
  Purchase #7 $34.61   8.594%   $37.5844   $37.58   $37.60   $37.60  
  7 purchase totals = $985.22       $1,076.5744   $1,076.57   $1,076.65   $1,076.60