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 $211.61   5.180%   $222.5714   $222.57   $222.55   $222.60  
  Purchase #2 $49.33   12.450%   $55.4716   $55.47   $55.45   $55.50  
  Purchase #3 $130.77   10.152%   $144.0458   $144.05   $144.05   $144.00  
  Purchase #4 $52.98   10.364%   $58.4708   $58.47   $58.45   $58.50  
  Purchase #5 $65.61   6.468%   $69.8537   $69.85   $69.85   $69.90  
  Purchase #6 $118.90   9.153%   $129.7829   $129.78   $129.80   $129.80  
  Purchase #7 $47.77   4.202%   $49.7773   $49.78   $49.80   $49.80  
  7 purchase totals = $676.97       $729.9735   $729.97   $729.95   $730.10