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 $194.81   3.170%   $200.9855   $200.99   $201.00   $201.00  
  Purchase #2 $45.88   4.308%   $47.8565   $47.86   $47.85   $47.90  
  Purchase #3 $34.55   7.128%   $37.0127   $37.01   $37.00   $37.00  
  Purchase #4 $22.48   7.421%   $24.1482   $24.15   $24.15   $24.10  
  Purchase #5 $166.53   6.622%   $177.5576   $177.56   $177.55   $177.60  
  Purchase #6 $184.25   7.438%   $197.9545   $197.95   $197.95   $198.00  
  Purchase #7 $196.49   11.154%   $218.4065   $218.41   $218.40   $218.40  
  7 purchase totals = $844.99       $903.9215   $903.93   $903.90   $904.00