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 $56.53   8.376%   $61.265   $61.27   $61.25   $61.30  
  Purchase #2 $74.34   6.508%   $79.178   $79.18   $79.20   $79.20  
  Purchase #3 $215.69   10.115%   $237.507   $237.51   $237.50   $237.50  
  Purchase #4 $249.38   12.847%   $281.4178   $281.42   $281.40   $281.40  
  Purchase #5 $88.61   7.792%   $95.5145   $95.51   $95.50   $95.50  
  Purchase #6 $205.73   5.627%   $217.3064   $217.31   $217.30   $217.30  
  Purchase #7 $29.30   4.808%   $30.7087   $30.71   $30.70   $30.70  
  7 purchase totals = $919.58       $1,002.8974   $1,002.91   $1,002.85   $1,002.90