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 $193.36   6.679%   $206.2745   $206.27   $206.25   $206.30  
  Purchase #2 $184.76   11.402%   $205.8263   $205.83   $205.85   $205.80  
  Purchase #3 $238.80   9.620%   $261.7726   $261.77   $261.75   $261.80  
  Purchase #4 $30.98   13.273%   $35.092   $35.09   $35.10   $35.10  
  Purchase #5 $128.35   3.288%   $132.5701   $132.57   $132.55   $132.60  
  Purchase #6 $178.33   8.835%   $194.0855   $194.09   $194.10   $194.10  
  Purchase #7 $180.50   5.647%   $190.6928   $190.69   $190.70   $190.70  
  7 purchase totals = $1,135.08       $1,226.3138   $1,226.31   $1,226.30   $1,226.40