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 $84.99   11.112%   $94.4341   $94.43   $94.45   $94.40  
  Purchase #2 $20.44   6.372%   $21.7424   $21.74   $21.75   $21.70  
  Purchase #3 $16.42   13.234%   $18.593   $18.59   $18.60   $18.60  
  Purchase #4 $82.71   6.573%   $88.1465   $88.15   $88.15   $88.10  
  Purchase #5 $119.41   12.677%   $134.5476   $134.55   $134.55   $134.50  
  Purchase #6 $217.61   11.172%   $241.9214   $241.92   $241.90   $241.90  
  Purchase #7 $194.48   6.305%   $206.742   $206.74   $206.75   $206.70  
  7 purchase totals = $736.06       $806.1270   $806.12   $806.15   $805.90