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 $93.52   5.140%   $98.3269   $98.33   $98.35   $98.30  
  Purchase #2 $110.63   8.446%   $119.9738   $119.97   $119.95   $120.00  
  Purchase #3 $112.49   10.292%   $124.0675   $124.07   $124.05   $124.10  
  Purchase #4 $246.65   4.789%   $258.4621   $258.46   $258.45   $258.50  
  Purchase #5 $21.35   3.296%   $22.0537   $22.05   $22.05   $22.10  
  Purchase #6 $160.70   11.472%   $179.1355   $179.14   $179.15   $179.10  
  Purchase #7 $18.35   8.514%   $19.9123   $19.91   $19.90   $19.90  
  7 purchase totals = $763.69       $821.9318   $821.93   $821.90   $822.00