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 $60.61   13.317%   $68.6814   $68.68   $68.70   $68.70  
  Purchase #2 $244.64   12.835%   $276.0395   $276.04   $276.05   $276.00  
  Purchase #3 $231.70   3.306%   $239.36   $239.36   $239.35   $239.40  
  Purchase #4 $226.96   9.248%   $247.9493   $247.95   $247.95   $247.90  
  Purchase #5 $245.78   10.831%   $272.4004   $272.40   $272.40   $272.40  
  Purchase #6 $12.91   7.405%   $13.866   $13.87   $13.85   $13.90  
  Purchase #7 $75.75   13.720%   $86.1429   $86.14   $86.15   $86.10  
  7 purchase totals = $1,098.35       $1,204.4395   $1,204.44   $1,204.45   $1,204.40