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	$74.82	9.735%	$82.1037	$82.10	$82.10	$82.10
Purchase #2	$166.92	13.658%	$189.7179	$189.72	$189.70	$189.70
Purchase #3	$86.77	3.530%	$89.833	$89.83	$89.85	$89.80
Purchase #4	$184.57	8.618%	$200.4762	$200.48	$200.50	$200.50
Purchase #5	$40.45	4.117%	$42.1153	$42.12	$42.10	$42.10
Purchase #6	$101.25	6.769%	$108.1036	$108.10	$108.10	$108.10
Purchase #7	$186.55	6.212%	$198.1385	$198.14	$198.15	$198.10
7 purchase totals =	$841.33		$910.4882	$910.49	$910.50	$910.40