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	$80.84	11.468%	$90.1107	$90.11	$90.10	$90.10
Purchase #2	$59.75	8.680%	$64.9363	$64.94	$64.95	$64.90
Purchase #3	$159.62	3.376%	$165.0088	$165.01	$165.00	$165.00
Purchase #4	$144.87	4.167%	$150.9067	$150.91	$150.90	$150.90
Purchase #5	$223.34	4.372%	$233.1044	$233.10	$233.10	$233.10
Purchase #6	$133.51	12.737%	$150.5152	$150.52	$150.50	$150.50
Purchase #7	$209.53	3.119%	$216.0652	$216.07	$216.05	$216.10
7 purchase totals =	$1,011.46		$1,070.6473	$1,070.66	$1,070.60	$1,070.60