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 $144.68   9.464%   $158.3725   $158.37   $158.35   $158.40  
  Purchase #2 $115.94   5.534%   $122.3561   $122.36   $122.35   $122.40  
  Purchase #3 $236.86   6.337%   $251.8698   $251.87   $251.85   $251.90  
  Purchase #4 $51.86   3.769%   $53.8146   $53.81   $53.80   $53.80  
  Purchase #5 $51.27   5.806%   $54.2467   $54.25   $54.25   $54.20  
  Purchase #6 $223.79   13.257%   $253.4578   $253.46   $253.45   $253.50  
  Purchase #7 $106.49   12.506%   $119.8076   $119.81   $119.80   $119.80  
  7 purchase totals = $930.89       $1,013.9251   $1,013.93   $1,013.85   $1,014.00