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 $151.93   3.317%   $156.9695   $156.97   $156.95   $157.00  
  Purchase #2 $229.96   6.299%   $244.4452   $244.45   $244.45   $244.40  
  Purchase #3 $86.95   11.517%   $96.964   $96.96   $96.95   $97.00  
  Purchase #4 $142.82   13.838%   $162.5834   $162.58   $162.60   $162.60  
  Purchase #5 $6.95   12.590%   $7.825   $7.83   $7.85   $7.80  
  Purchase #6 $192.98   13.430%   $218.8972   $218.90   $218.90   $218.90  
  Purchase #7 $33.49   10.302%   $36.9401   $36.94   $36.95   $36.90  
  7 purchase totals = $845.08       $924.6244   $924.63   $924.65   $924.60