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 $223.92   13.771%   $254.756   $254.76   $254.75   $254.80  
  Purchase #2 $187.55   3.790%   $194.6581   $194.66   $194.65   $194.70  
  Purchase #3 $78.76   10.475%   $87.0101   $87.01   $87.00   $87.00  
  Purchase #4 $230.42   8.361%   $249.6854   $249.69   $249.70   $249.70  
  Purchase #5 $50.77   7.473%   $54.564   $54.56   $54.55   $54.60  
  Purchase #6 $191.26   12.325%   $214.8328   $214.83   $214.85   $214.80  
  Purchase #7 $12.46   12.639%   $14.0348   $14.03   $14.05   $14.00  
  7 purchase totals = $975.14       $1,069.5412   $1,069.54   $1,069.55   $1,069.60