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 $184.86   12.662%   $208.267   $208.27   $208.25   $208.30  
  Purchase #2 $134.74   11.778%   $150.6097   $150.61   $150.60   $150.60  
  Purchase #3 $114.53   8.526%   $124.2948   $124.29   $124.30   $124.30  
  Purchase #4 $247.42   6.342%   $263.1114   $263.11   $263.10   $263.10  
  Purchase #5 $143.45   4.125%   $149.3673   $149.37   $149.35   $149.40  
  Purchase #6 $10.78   9.427%   $11.7962   $11.80   $11.80   $11.80  
  Purchase #7 $219.38   11.186%   $243.9198   $243.92   $243.90   $243.90  
  7 purchase totals = $1,055.16       $1,151.3662   $1,151.37   $1,151.30   $1,151.40