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 $188.60   4.211%   $196.5419   $196.54   $196.55   $196.50  
  Purchase #2 $181.93   9.677%   $199.5354   $199.54   $199.55   $199.50  
  Purchase #3 $80.29   5.199%   $84.4643   $84.46   $84.45   $84.50  
  Purchase #4 $229.86   12.408%   $258.381   $258.38   $258.40   $258.40  
  Purchase #5 $69.69   6.487%   $74.2108   $74.21   $74.20   $74.20  
  Purchase #6 $19.73   13.695%   $22.432   $22.43   $22.45   $22.40  
  Purchase #7 $54.53   11.117%   $60.5921   $60.59   $60.60   $60.60  
  7 purchase totals = $824.63       $896.1575   $896.15   $896.20   $896.10