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 $200.92   3.505%   $207.9622   $207.96   $207.95   $208.00  
  Purchase #2 $44.67   4.355%   $46.6154   $46.62   $46.60   $46.60  
  Purchase #3 $69.51   6.457%   $73.9983   $74.00   $74.00   $74.00  
  Purchase #4 $187.64   12.603%   $211.2883   $211.29   $211.30   $211.30  
  Purchase #5 $87.34   8.656%   $94.9002   $94.90   $94.90   $94.90  
  Purchase #6 $99.51   13.749%   $113.1916   $113.19   $113.20   $113.20  
  Purchase #7 $74.69   11.455%   $83.2457   $83.25   $83.25   $83.20  
  7 purchase totals = $764.28       $831.2017   $831.21   $831.20   $831.20