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 $212.79   5.476%   $224.4424   $224.44   $224.45   $224.40  
  Purchase #2 $33.89   3.544%   $35.0911   $35.09   $35.10   $35.10  
  Purchase #3 $83.74   11.591%   $93.4463   $93.45   $93.45   $93.40  
  Purchase #4 $187.94   13.807%   $213.8889   $213.89   $213.90   $213.90  
  Purchase #5 $232.95   6.540%   $248.1849   $248.18   $248.20   $248.20  
  Purchase #6 $47.53   8.168%   $51.4123   $51.41   $51.40   $51.40  
  Purchase #7 $244.65   6.230%   $259.8917   $259.89   $259.90   $259.90  
  7 purchase totals = $1,043.49       $1,126.3576   $1,126.35   $1,126.40   $1,126.30