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 $38.85   11.724%   $43.4048   $43.40   $43.40   $43.40  
  Purchase #2 $178.97   13.120%   $202.4509   $202.45   $202.45   $202.50  
  Purchase #3 $221.95   9.287%   $242.5625   $242.56   $242.55   $242.60  
  Purchase #4 $61.78   5.479%   $65.1649   $65.16   $65.15   $65.20  
  Purchase #5 $155.54   5.575%   $164.2114   $164.21   $164.20   $164.20  
  Purchase #6 $6.61   12.127%   $7.4116   $7.41   $7.40   $7.40  
  Purchase #7 $239.86   9.667%   $263.0473   $263.05   $263.05   $263.00  
  7 purchase totals = $903.56       $988.2534   $988.24   $988.20   $988.30