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 $58.28   5.181%   $61.2995   $61.30   $61.30   $61.30  
  Purchase #2 $16.59   9.508%   $18.1674   $18.17   $18.15   $18.20  
  Purchase #3 $136.48   7.595%   $146.8457   $146.85   $146.85   $146.80  
  Purchase #4 $170.51   13.710%   $193.8869   $193.89   $193.90   $193.90  
  Purchase #5 $158.41   13.710%   $180.128   $180.13   $180.15   $180.10  
  Purchase #6 $249.57   7.756%   $268.9266   $268.93   $268.95   $268.90  
  Purchase #7 $90.40   6.335%   $96.1268   $96.13   $96.15   $96.10  
  7 purchase totals = $880.24       $965.3809   $965.40   $965.45   $965.30