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 $6.90   7.149%   $7.3933   $7.39   $7.40   $7.40  
  Purchase #2 $80.30   12.690%   $90.4901   $90.49   $90.50   $90.50  
  Purchase #3 $174.30   6.547%   $185.7114   $185.71   $185.70   $185.70  
  Purchase #4 $40.99   7.841%   $44.204   $44.20   $44.20   $44.20  
  Purchase #5 $36.88   11.661%   $41.1806   $41.18   $41.20   $41.20  
  Purchase #6 $149.80   13.601%   $170.1743   $170.17   $170.15   $170.20  
  Purchase #7 $214.48   3.263%   $221.4785   $221.48   $221.50   $221.50  
  7 purchase totals = $703.65       $760.6322   $760.62   $760.65   $760.70