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 $56.85   6.356%   $60.4634   $60.46   $60.45   $60.50  
  Purchase #2 $109.79   11.306%   $122.2029   $122.20   $122.20   $122.20  
  Purchase #3 $92.40   9.334%   $101.0246   $101.02   $101.00   $101.00  
  Purchase #4 $243.93   13.431%   $276.6922   $276.69   $276.70   $276.70  
  Purchase #5 $50.51   12.123%   $56.6333   $56.63   $56.65   $56.60  
  Purchase #6 $166.41   9.637%   $182.4469   $182.45   $182.45   $182.40  
  Purchase #7 $245.59   10.574%   $271.5587   $271.56   $271.55   $271.60  
  7 purchase totals = $965.48       $1,071.0220   $1,071.01   $1,071.00   $1,071.00