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	$63.51	12.209%	$71.2639	$71.26	$71.25	$71.30
Purchase #2	$86.64	3.311%	$89.5087	$89.51	$89.50	$89.50
Purchase #3	$100.45	4.793%	$105.2646	$105.26	$105.25	$105.30
Purchase #4	$188.39	11.282%	$209.6442	$209.64	$209.65	$209.60
Purchase #5	$94.49	13.524%	$107.2688	$107.27	$107.25	$107.30
Purchase #6	$52.79	3.580%	$54.6799	$54.68	$54.70	$54.70
Purchase #7	$19.33	6.701%	$20.6253	$20.63	$20.65	$20.60
7 purchase totals =	$605.60		$658.2554	$658.25	$658.25	$658.30