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 $55.29   11.254%   $61.5123   $61.51   $61.50   $61.50  
  Purchase #2 $234.95   11.766%   $262.5942   $262.59   $262.60   $262.60  
  Purchase #3 $203.34   4.414%   $212.3154   $212.32   $212.30   $212.30  
  Purchase #4 $207.60   6.634%   $221.3722   $221.37   $221.35   $221.40  
  Purchase #5 $176.33   10.645%   $195.1003   $195.10   $195.10   $195.10  
  Purchase #6 $206.90   11.264%   $230.2052   $230.21   $230.20   $230.20  
  Purchase #7 $15.57   8.377%   $16.8743   $16.87   $16.85   $16.90  
  7 purchase totals = $1,099.98       $1,199.9739   $1,199.97   $1,199.90   $1,200.00