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	$80.51	6.702%	$85.9058	$85.91	$85.90	$85.90
Purchase #2	$85.51	3.331%	$88.3583	$88.36	$88.35	$88.40
Purchase #3	$235.43	13.788%	$267.8911	$267.89	$267.90	$267.90
Purchase #4	$230.78	11.575%	$257.4928	$257.49	$257.50	$257.50
Purchase #5	$221.85	3.123%	$228.7784	$228.78	$228.80	$228.80
Purchase #6	$235.62	5.678%	$248.9985	$249.00	$249.00	$249.00
Purchase #7	$112.46	9.570%	$123.2224	$123.22	$123.20	$123.20
7 purchase totals =	$1,202.16		$1,300.6473	$1,300.65	$1,300.65	$1,300.70