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 $146.94   6.447%   $156.4132   $156.41   $156.40   $156.40  
  Purchase #2 $65.59   11.386%   $73.0581   $73.06   $73.05   $73.10  
  Purchase #3 $244.39   6.735%   $260.8497   $260.85   $260.85   $260.80  
  Purchase #4 $164.70   6.630%   $175.6196   $175.62   $175.60   $175.60  
  Purchase #5 $73.51   11.370%   $81.8681   $81.87   $81.85   $81.90  
  Purchase #6 $232.99   8.816%   $253.5304   $253.53   $253.55   $253.50  
  Purchase #7 $240.36   9.668%   $263.598   $263.60   $263.60   $263.60  
  7 purchase totals = $1,168.48       $1,264.9371   $1,264.94   $1,264.90   $1,264.90