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 $83.40   3.335%   $86.1814   $86.18   $86.20   $86.20  
  Purchase #2 $149.57   4.365%   $156.0987   $156.10   $156.10   $156.10  
  Purchase #3 $96.56   10.413%   $106.6148   $106.61   $106.60   $106.60  
  Purchase #4 $214.39   8.839%   $233.3399   $233.34   $233.35   $233.30  
  Purchase #5 $82.38   6.507%   $87.7405   $87.74   $87.75   $87.70  
  Purchase #6 $182.91   8.221%   $197.947   $197.95   $197.95   $197.90  
  Purchase #7 $7.55   5.429%   $7.9599   $7.96   $7.95   $8.00  
  7 purchase totals = $816.76       $875.8822   $875.88   $875.90   $875.80