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 $95.80   8.834%   $104.263   $104.26   $104.25   $104.30  
  Purchase #2 $33.72   8.645%   $36.6351   $36.64   $36.65   $36.60  
  Purchase #3 $160.84   5.240%   $169.268   $169.27   $169.25   $169.30  
  Purchase #4 $73.26   5.801%   $77.5098   $77.51   $77.50   $77.50  
  Purchase #5 $158.29   3.192%   $163.3426   $163.34   $163.35   $163.30  
  Purchase #6 $146.48   4.426%   $152.9632   $152.96   $152.95   $153.00  
  Purchase #7 $47.94   6.816%   $51.2076   $51.21   $51.20   $51.20  
  7 purchase totals = $716.33       $755.1893   $755.19   $755.15   $755.20