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 $197.36   4.374%   $205.9925   $205.99   $206.00   $206.00  
  Purchase #2 $250.52   6.126%   $265.8669   $265.87   $265.85   $265.90  
  Purchase #3 $232.87   6.188%   $247.28   $247.28   $247.30   $247.30  
  Purchase #4 $140.39   8.276%   $152.0087   $152.01   $152.00   $152.00  
  Purchase #5 $230.26   10.622%   $254.7182   $254.72   $254.70   $254.70  
  Purchase #6 $76.96   6.607%   $82.0447   $82.04   $82.05   $82.00  
  Purchase #7 $138.67   9.401%   $151.7064   $151.71   $151.70   $151.70  
  7 purchase totals = $1,267.03       $1,359.6174   $1,359.62   $1,359.60   $1,359.60