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 $162.75   12.690%   $183.403   $183.40   $183.40   $183.40  
  Purchase #2 $61.71   4.865%   $64.7122   $64.71   $64.70   $64.70  
  Purchase #3 $147.33   5.351%   $155.2136   $155.21   $155.20   $155.20  
  Purchase #4 $195.59   6.130%   $207.5797   $207.58   $207.60   $207.60  
  Purchase #5 $93.83   10.762%   $103.928   $103.93   $103.95   $103.90  
  Purchase #6 $141.49   7.705%   $152.3918   $152.39   $152.40   $152.40  
  Purchase #7 $88.44   8.289%   $95.7708   $95.77   $95.75   $95.80  
  7 purchase totals = $891.14       $962.9991   $962.99   $963.00   $963.00