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 $34.63   4.226%   $36.0935   $36.09   $36.10   $36.10  
  Purchase #2 $134.71   6.335%   $143.2439   $143.24   $143.25   $143.20  
  Purchase #3 $123.38   8.479%   $133.8414   $133.84   $133.85   $133.80  
  Purchase #4 $187.72   4.663%   $196.4734   $196.47   $196.45   $196.50  
  Purchase #5 $227.94   9.202%   $248.915   $248.92   $248.90   $248.90  
  Purchase #6 $26.87   7.546%   $28.8976   $28.90   $28.90   $28.90  
  Purchase #7 $58.48   9.751%   $64.1824   $64.18   $64.20   $64.20  
  7 purchase totals = $793.73       $851.6472   $851.64   $851.65   $851.60