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 $119.65   6.298%   $127.1856   $127.19   $127.20   $127.20  
  Purchase #2 $54.27   11.758%   $60.6511   $60.65   $60.65   $60.70  
  Purchase #3 $23.75   9.448%   $25.9939   $25.99   $26.00   $26.00  
  Purchase #4 $236.43   8.437%   $256.3776   $256.38   $256.40   $256.40  
  Purchase #5 $49.97   7.795%   $53.8652   $53.87   $53.85   $53.90  
  Purchase #6 $72.60   4.404%   $75.7973   $75.80   $75.80   $75.80  
  Purchase #7 $187.80   5.417%   $197.9731   $197.97   $197.95   $198.00  
  7 purchase totals = $744.47       $797.8438   $797.85   $797.85   $798.00