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 $61.92   12.822%   $69.8594   $69.86   $69.85   $69.90  
  Purchase #2 $108.84   5.616%   $114.9525   $114.95   $114.95   $115.00  
  Purchase #3 $115.37   4.720%   $120.8155   $120.82   $120.80   $120.80  
  Purchase #4 $182.78   6.134%   $193.9917   $193.99   $194.00   $194.00  
  Purchase #5 $221.48   8.600%   $240.5273   $240.53   $240.55   $240.50  
  Purchase #6 $175.34   5.687%   $185.3116   $185.31   $185.30   $185.30  
  Purchase #7 $37.96   8.569%   $41.2128   $41.21   $41.20   $41.20  
  7 purchase totals = $903.69       $966.6708   $966.67   $966.65   $966.70