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 $227.64   11.221%   $253.1835   $253.18   $253.20   $253.20  
  Purchase #2 $172.86   10.112%   $190.3396   $190.34   $190.35   $190.30  
  Purchase #3 $217.88   12.852%   $245.8819   $245.88   $245.90   $245.90  
  Purchase #4 $96.85   9.452%   $106.0043   $106.00   $106.00   $106.00  
  Purchase #5 $243.26   12.799%   $274.3948   $274.39   $274.40   $274.40  
  Purchase #6 $26.47   12.708%   $29.8338   $29.83   $29.85   $29.80  
  Purchase #7 $210.99   10.797%   $233.7706   $233.77   $233.75   $233.80  
  7 purchase totals = $1,195.95       $1,333.4085   $1,333.39   $1,333.45   $1,333.40