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 $194.68   12.365%   $218.7522   $218.75   $218.75   $218.80  
  Purchase #2 $210.84   12.180%   $236.5203   $236.52   $236.50   $236.50  
  Purchase #3 $51.45   7.561%   $55.3401   $55.34   $55.35   $55.30  
  Purchase #4 $226.76   3.404%   $234.4789   $234.48   $234.50   $234.50  
  Purchase #5 $248.39   4.741%   $260.1662   $260.17   $260.15   $260.20  
  Purchase #6 $34.38   7.508%   $36.9613   $36.96   $36.95   $37.00  
  Purchase #7 $57.91   8.799%   $63.0055   $63.01   $63.00   $63.00  
  7 purchase totals = $1,024.41       $1,105.2245   $1,105.23   $1,105.20   $1,105.30