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 $157.48   10.862%   $174.5855   $174.59   $174.60   $174.60  
  Purchase #2 $240.41   11.129%   $267.1652   $267.17   $267.15   $267.20  
  Purchase #3 $247.31   6.535%   $263.4717   $263.47   $263.45   $263.50  
  Purchase #4 $9.32   6.781%   $9.952   $9.95   $9.95   $10.00  
  Purchase #5 $101.85   10.221%   $112.2601   $112.26   $112.25   $112.30  
  Purchase #6 $68.76   8.808%   $74.8164   $74.82   $74.80   $74.80  
  Purchase #7 $61.50   8.188%   $66.5356   $66.54   $66.55   $66.50  
  7 purchase totals = $886.63       $968.7865   $968.80   $968.75   $968.90