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 $213.35   4.594%   $223.1513   $223.15   $223.15   $223.20  
  Purchase #2 $47.57   3.782%   $49.3691   $49.37   $49.35   $49.40  
  Purchase #3 $188.64   5.726%   $199.4415   $199.44   $199.45   $199.40  
  Purchase #4 $129.64   13.519%   $147.166   $147.17   $147.15   $147.20  
  Purchase #5 $29.93   13.381%   $33.9349   $33.93   $33.95   $33.90  
  Purchase #6 $51.90   5.125%   $54.5599   $54.56   $54.55   $54.60  
  Purchase #7 $151.67   11.323%   $168.8436   $168.84   $168.85   $168.80  
  7 purchase totals = $812.70       $876.4663   $876.46   $876.45   $876.50