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 $191.64   7.143%   $205.3288   $205.33   $205.35   $205.30  
  Purchase #2 $143.93   7.321%   $154.4671   $154.47   $154.45   $154.50  
  Purchase #3 $85.91   11.142%   $95.4821   $95.48   $95.50   $95.50  
  Purchase #4 $237.37   5.537%   $250.5132   $250.51   $250.50   $250.50  
  Purchase #5 $84.49   11.715%   $94.388   $94.39   $94.40   $94.40  
  Purchase #6 $66.97   4.183%   $69.7714   $69.77   $69.75   $69.80  
  Purchase #7 $183.45   11.595%   $204.721   $204.72   $204.70   $204.70  
  7 purchase totals = $993.76       $1,074.6716   $1,074.67   $1,074.65   $1,074.70