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	$18.71	9.187%	$20.4289	$20.43	$20.45	$20.40
Purchase #2	$38.55	7.585%	$41.474	$41.47	$41.45	$41.50
Purchase #3	$166.72	9.569%	$182.6734	$182.67	$182.65	$182.70
Purchase #4	$209.72	4.628%	$219.4258	$219.43	$219.45	$219.40
Purchase #5	$9.99	13.461%	$11.3348	$11.33	$11.35	$11.30
Purchase #6	$235.50	9.698%	$258.3388	$258.34	$258.35	$258.30
Purchase #7	$83.77	7.647%	$90.1759	$90.18	$90.20	$90.20
7 purchase totals =	$762.96		$823.8516	$823.85	$823.90	$823.80