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 $49.34   9.658%   $54.1053   $54.11   $54.10   $54.10  
  Purchase #2 $132.75   8.616%   $144.1877   $144.19   $144.20   $144.20  
  Purchase #3 $248.47   9.121%   $271.1329   $271.13   $271.15   $271.10  
  Purchase #4 $61.90   7.150%   $66.3259   $66.33   $66.35   $66.30  
  Purchase #5 $83.66   13.254%   $94.7483   $94.75   $94.75   $94.70  
  Purchase #6 $94.49   5.778%   $99.9496   $99.95   $99.95   $99.90  
  Purchase #7 $183.90   6.126%   $195.1657   $195.17   $195.15   $195.20  
  7 purchase totals = $854.51       $925.6154   $925.63   $925.65   $925.50