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	$223.35	5.704%	$236.0899	$236.09	$236.10	$236.10
Purchase #2	$124.65	4.171%	$129.8492	$129.85	$129.85	$129.80
Purchase #3	$123.54	6.546%	$131.6269	$131.63	$131.65	$131.60
Purchase #4	$139.74	11.131%	$155.2945	$155.29	$155.30	$155.30
Purchase #5	$118.66	7.450%	$127.5002	$127.50	$127.50	$127.50
Purchase #6	$131.63	8.554%	$142.8896	$142.89	$142.90	$142.90
Purchase #7	$20.25	3.801%	$21.0197	$21.02	$21.00	$21.00
7 purchase totals =	$881.82		$944.2700	$944.27	$944.30	$944.20