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 $96.31   5.478%   $101.5859   $101.59   $101.60   $101.60  
  Purchase #2 $241.36   11.718%   $269.6426   $269.64   $269.65   $269.60  
  Purchase #3 $159.43   6.182%   $169.286   $169.29   $169.30   $169.30  
  Purchase #4 $16.68   5.664%   $17.6248   $17.62   $17.60   $17.60  
  Purchase #5 $130.75   9.102%   $142.6509   $142.65   $142.65   $142.70  
  Purchase #6 $58.66   11.554%   $65.4376   $65.44   $65.45   $65.40  
  Purchase #7 $15.74   6.320%   $16.7348   $16.73   $16.75   $16.70  
  7 purchase totals = $718.93       $782.9626   $782.96   $783.00   $782.90