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 $38.81   6.549%   $41.3517   $41.35   $41.35   $41.40  
  Purchase #2 $214.83   9.311%   $234.8328   $234.83   $234.85   $234.80  
  Purchase #3 $34.80   6.297%   $36.9914   $36.99   $37.00   $37.00  
  Purchase #4 $54.87   11.551%   $61.208   $61.21   $61.20   $61.20  
  Purchase #5 $199.97   6.816%   $213.6   $213.60   $213.60   $213.60  
  Purchase #6 $248.97   8.343%   $269.7416   $269.74   $269.75   $269.70  
  Purchase #7 $56.82   3.553%   $58.8388   $58.84   $58.85   $58.80  
  7 purchase totals = $849.07       $916.5643   $916.56   $916.60   $916.50