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 $48.27   12.363%   $54.2376   $54.24   $54.25   $54.20  
  Purchase #2 $57.79   12.532%   $65.0322   $65.03   $65.05   $65.00  
  Purchase #3 $115.42   8.152%   $124.829   $124.83   $124.85   $124.80  
  Purchase #4 $205.73   8.383%   $222.9763   $222.98   $223.00   $223.00  
  Purchase #5 $16.44   3.585%   $17.0294   $17.03   $17.05   $17.00  
  Purchase #6 $146.50   5.113%   $153.9905   $153.99   $154.00   $154.00  
  Purchase #7 $149.27   5.692%   $157.7664   $157.77   $157.75   $157.80  
  7 purchase totals = $739.42       $795.8614   $795.87   $795.95   $795.80