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 $198.62   3.725%   $206.0186   $206.02   $206.00   $206.00  
  Purchase #2 $69.48   5.117%   $73.0353   $73.04   $73.05   $73.00  
  Purchase #3 $197.89   10.231%   $218.1361   $218.14   $218.15   $218.10  
  Purchase #4 $183.85   11.522%   $205.0332   $205.03   $205.05   $205.00  
  Purchase #5 $185.71   9.169%   $202.7377   $202.74   $202.75   $202.70  
  Purchase #6 $8.57   4.487%   $8.9545   $8.95   $8.95   $9.00  
  Purchase #7 $141.56   3.569%   $146.6123   $146.61   $146.60   $146.60  
  7 purchase totals = $985.68       $1,060.5277   $1,060.53   $1,060.55   $1,060.40