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	$125.31	7.294%	$134.4501	$134.45	$134.45	$134.50
Purchase #2	$75.61	13.638%	$85.9217	$85.92	$85.90	$85.90
Purchase #3	$10.33	11.283%	$11.4955	$11.50	$11.50	$11.50
Purchase #4	$154.33	5.166%	$162.3027	$162.30	$162.30	$162.30
Purchase #5	$148.31	11.370%	$165.1728	$165.17	$165.15	$165.20
Purchase #6	$59.29	5.440%	$62.5154	$62.52	$62.50	$62.50
Purchase #7	$28.60	10.717%	$31.6651	$31.67	$31.65	$31.70
7 purchase totals =	$601.78		$653.5233	$653.53	$653.45	$653.60