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	$244.87	6.335%	$260.3825	$260.38	$260.40	$260.40
Purchase #2	$53.41	11.869%	$59.7492	$59.75	$59.75	$59.70
Purchase #3	$102.32	11.215%	$113.7952	$113.80	$113.80	$113.80
Purchase #4	$93.27	13.391%	$105.7598	$105.76	$105.75	$105.80
Purchase #5	$61.79	9.228%	$67.492	$67.49	$67.50	$67.50
Purchase #6	$224.92	10.646%	$248.865	$248.87	$248.85	$248.90
Purchase #7	$60.64	10.575%	$67.0527	$67.05	$67.05	$67.10
7 purchase totals =	$841.22		$923.0964	$923.10	$923.10	$923.20