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	$228.99	11.579%	$255.5048	$255.50	$255.50	$255.50
Purchase #2	$85.57	4.117%	$89.0929	$89.09	$89.10	$89.10
Purchase #3	$88.35	6.508%	$94.0998	$94.10	$94.10	$94.10
Purchase #4	$190.74	12.468%	$214.5215	$214.52	$214.50	$214.50
Purchase #5	$149.84	7.626%	$161.2668	$161.27	$161.25	$161.30
Purchase #6	$71.33	3.591%	$73.8915	$73.89	$73.90	$73.90
Purchase #7	$36.96	4.130%	$38.4864	$38.49	$38.50	$38.50
7 purchase totals =	$851.78		$926.8637	$926.86	$926.85	$926.90