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 $175.83   9.146%   $191.9114   $191.91   $191.90   $191.90  
  Purchase #2 $169.87   4.175%   $176.9621   $176.96   $176.95   $177.00  
  Purchase #3 $44.41   12.415%   $49.9235   $49.92   $49.90   $49.90  
  Purchase #4 $42.86   10.296%   $47.2729   $47.27   $47.25   $47.30  
  Purchase #5 $36.30   10.694%   $40.1819   $40.18   $40.20   $40.20  
  Purchase #6 $152.81   10.659%   $169.098   $169.10   $169.10   $169.10  
  Purchase #7 $64.63   11.588%   $72.1193   $72.12   $72.10   $72.10  
  7 purchase totals = $686.71       $747.4691   $747.46   $747.40   $747.50