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	$89.62	5.261%	$94.3349	$94.33	$94.35	$94.30
Purchase #2	$130.89	11.751%	$146.2709	$146.27	$146.25	$146.30
Purchase #3	$68.61	6.276%	$72.916	$72.92	$72.90	$72.90
Purchase #4	$205.65	8.274%	$222.6655	$222.67	$222.65	$222.70
Purchase #5	$16.25	13.433%	$18.4329	$18.43	$18.45	$18.40
Purchase #6	$113.78	6.158%	$120.7866	$120.79	$120.80	$120.80
Purchase #7	$181.42	12.616%	$204.3079	$204.31	$204.30	$204.30
7 purchase totals =	$806.22		$879.7147	$879.72	$879.70	$879.70