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 $232.29   6.209%   $246.7129   $246.71   $246.70   $246.70  
  Purchase #2 $158.99   5.741%   $168.1176   $168.12   $168.10   $168.10  
  Purchase #3 $126.70   12.674%   $142.758   $142.76   $142.75   $142.80  
  Purchase #4 $36.73   10.609%   $40.6267   $40.63   $40.65   $40.60  
  Purchase #5 $49.57   8.153%   $53.6114   $53.61   $53.60   $53.60  
  Purchase #6 $154.58   4.486%   $161.5145   $161.51   $161.50   $161.50  
  Purchase #7 $192.39   5.470%   $202.9137   $202.91   $202.90   $202.90  
  7 purchase totals = $951.25       $1,016.2548   $1,016.25   $1,016.20   $1,016.20