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 $32.71   6.828%   $34.9434   $34.94   $34.95   $34.90  
  Purchase #2 $123.43   11.420%   $137.5257   $137.53   $137.55   $137.50  
  Purchase #3 $232.71   11.751%   $260.0558   $260.06   $260.05   $260.10  
  Purchase #4 $22.41   6.629%   $23.8956   $23.90   $23.90   $23.90  
  Purchase #5 $94.35   13.851%   $107.4184   $107.42   $107.40   $107.40  
  Purchase #6 $165.27   3.139%   $170.4578   $170.46   $170.45   $170.50  
  Purchase #7 $239.86   3.392%   $247.9961   $248.00   $248.00   $248.00  
  7 purchase totals = $910.74       $982.2928   $982.31   $982.30   $982.30