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 $245.98   8.202%   $266.1553   $266.16   $266.15   $266.20  
  Purchase #2 $15.61   9.852%   $17.1479   $17.15   $17.15   $17.10  
  Purchase #3 $186.59   9.389%   $204.1089   $204.11   $204.10   $204.10  
  Purchase #4 $24.26   8.377%   $26.2923   $26.29   $26.30   $26.30  
  Purchase #5 $98.49   10.664%   $108.993   $108.99   $109.00   $109.00  
  Purchase #6 $47.96   12.853%   $54.1243   $54.12   $54.10   $54.10  
  Purchase #7 $243.67   8.777%   $265.0569   $265.06   $265.05   $265.10  
  7 purchase totals = $862.56       $941.8786   $941.88   $941.85   $941.90