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 $14.80   6.361%   $15.7414   $15.74   $15.75   $15.70  
  Purchase #2 $121.61   3.323%   $125.6511   $125.65   $125.65   $125.70  
  Purchase #3 $191.35   5.276%   $201.4456   $201.45   $201.45   $201.40  
  Purchase #4 $48.43   4.724%   $50.7178   $50.72   $50.70   $50.70  
  Purchase #5 $111.89   3.219%   $115.4917   $115.49   $115.50   $115.50  
  Purchase #6 $101.99   9.395%   $111.572   $111.57   $111.55   $111.60  
  Purchase #7 $18.32   11.565%   $20.4387   $20.44   $20.45   $20.40  
  7 purchase totals = $608.39       $641.0583   $641.06   $641.05   $641.00