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 $54.98   9.570%   $60.2416   $60.24   $60.25   $60.20  
  Purchase #2 $220.74   6.448%   $234.9733   $234.97   $234.95   $235.00  
  Purchase #3 $228.81   10.807%   $253.5375   $253.54   $253.55   $253.50  
  Purchase #4 $91.92   4.191%   $95.7724   $95.77   $95.75   $95.80  
  Purchase #5 $139.30   13.805%   $158.5304   $158.53   $158.55   $158.50  
  Purchase #6 $31.56   7.598%   $33.9579   $33.96   $33.95   $34.00  
  Purchase #7 $107.65   9.720%   $118.1136   $118.11   $118.10   $118.10  
  7 purchase totals = $874.96       $955.1267   $955.12   $955.10   $955.10