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 $57.70   7.642%   $62.1094   $62.11   $62.10   $62.10  
  Purchase #2 $191.44   11.288%   $213.0497   $213.05   $213.05   $213.00  
  Purchase #3 $122.38   4.405%   $127.7708   $127.77   $127.75   $127.80  
  Purchase #4 $13.54   4.760%   $14.1845   $14.18   $14.20   $14.20  
  Purchase #5 $30.40   10.304%   $33.5324   $33.53   $33.55   $33.50  
  Purchase #6 $178.79   12.719%   $201.5303   $201.53   $201.55   $201.50  
  Purchase #7 $77.57   5.353%   $81.7223   $81.72   $81.70   $81.70  
  7 purchase totals = $671.82       $733.8994   $733.89   $733.90   $733.80