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 $109.76   4.735%   $114.9571   $114.96   $114.95   $115.00  
  Purchase #2 $180.71   12.544%   $203.3783   $203.38   $203.40   $203.40  
  Purchase #3 $173.55   4.530%   $181.4118   $181.41   $181.40   $181.40  
  Purchase #4 $68.79   6.809%   $73.4739   $73.47   $73.45   $73.50  
  Purchase #5 $239.50   11.270%   $266.4917   $266.49   $266.50   $266.50  
  Purchase #6 $68.40   4.824%   $71.6996   $71.70   $71.70   $71.70  
  Purchase #7 $13.41   11.840%   $14.9977   $15.00   $15.00   $15.00  
  7 purchase totals = $854.12       $926.4101   $926.41   $926.40   $926.50