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 $87.63   5.513%   $92.461   $92.46   $92.45   $92.50  
  Purchase #2 $241.27   3.168%   $248.9134   $248.91   $248.90   $248.90  
  Purchase #3 $87.35   8.303%   $94.6027   $94.60   $94.60   $94.60  
  Purchase #4 $213.91   13.709%   $243.2349   $243.23   $243.25   $243.20  
  Purchase #5 $215.40   7.553%   $231.6692   $231.67   $231.65   $231.70  
  Purchase #6 $179.64   11.168%   $199.7022   $199.70   $199.70   $199.70  
  Purchase #7 $244.88   4.599%   $256.142   $256.14   $256.15   $256.10  
  7 purchase totals = $1,270.08       $1,366.7254   $1,366.71   $1,366.70   $1,366.70