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 $48.90   11.669%   $54.6061   $54.61   $54.60   $54.60  
  Purchase #2 $213.97   3.272%   $220.9711   $220.97   $220.95   $221.00  
  Purchase #3 $118.30   10.473%   $130.6896   $130.69   $130.70   $130.70  
  Purchase #4 $86.71   12.632%   $97.6632   $97.66   $97.65   $97.70  
  Purchase #5 $187.35   3.185%   $193.3171   $193.32   $193.30   $193.30  
  Purchase #6 $7.84   7.195%   $8.4041   $8.40   $8.40   $8.40  
  Purchase #7 $25.62   4.271%   $26.7142   $26.71   $26.70   $26.70  
  7 purchase totals = $688.69       $732.3654   $732.36   $732.30   $732.40