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	$20.61	4.478%	$21.5329	$21.53	$21.55	$21.50
Purchase #2	$218.90	8.746%	$238.045	$238.05	$238.05	$238.00
Purchase #3	$119.46	6.727%	$127.4961	$127.50	$127.50	$127.50
Purchase #4	$128.82	10.119%	$141.8553	$141.86	$141.85	$141.90
Purchase #5	$113.55	3.704%	$117.7559	$117.76	$117.75	$117.80
Purchase #6	$210.41	12.391%	$236.4819	$236.48	$236.50	$236.50
Purchase #7	$199.68	9.216%	$218.0825	$218.08	$218.10	$218.10
7 purchase totals =	$1,011.43		$1,101.2496	$1,101.26	$1,101.30	$1,101.30