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 $189.83   7.466%   $204.0027   $204.00   $204.00   $204.00  
  Purchase #2 $192.47   6.836%   $205.6272   $205.63   $205.65   $205.60  
  Purchase #3 $212.85   8.279%   $230.4719   $230.47   $230.45   $230.50  
  Purchase #4 $153.54   6.747%   $163.8993   $163.90   $163.90   $163.90  
  Purchase #5 $11.35   13.716%   $12.9068   $12.91   $12.90   $12.90  
  Purchase #6 $128.85   5.694%   $136.1867   $136.19   $136.20   $136.20  
  Purchase #7 $67.71   11.636%   $75.5887   $75.59   $75.60   $75.60  
  7 purchase totals = $956.60       $1,028.6833   $1,028.69   $1,028.70   $1,028.70