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 $54.59   11.328%   $60.774   $60.77   $60.75   $60.80  
  Purchase #2 $40.91   6.595%   $43.608   $43.61   $43.60   $43.60  
  Purchase #3 $117.33   13.645%   $133.3397   $133.34   $133.35   $133.30  
  Purchase #4 $184.40   6.518%   $196.4192   $196.42   $196.40   $196.40  
  Purchase #5 $179.99   13.736%   $204.7134   $204.71   $204.70   $204.70  
  Purchase #6 $132.86   10.134%   $146.324   $146.32   $146.30   $146.30  
  Purchase #7 $155.71   8.307%   $168.6448   $168.64   $168.65   $168.60  
  7 purchase totals = $865.79       $953.8231   $953.81   $953.75   $953.70