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	$200.87	11.248%	$223.4639	$223.46	$223.45	$223.50
Purchase #2	$120.60	4.385%	$125.8883	$125.89	$125.90	$125.90
Purchase #3	$145.99	9.318%	$159.5933	$159.59	$159.60	$159.60
Purchase #4	$50.91	9.729%	$55.863	$55.86	$55.85	$55.90
Purchase #5	$146.45	12.832%	$165.2425	$165.24	$165.25	$165.20
Purchase #6	$79.44	3.758%	$82.4254	$82.43	$82.45	$82.40
Purchase #7	$175.50	3.453%	$181.56	$181.56	$181.55	$181.60
7 purchase totals =	$919.76		$994.0364	$994.03	$994.05	$994.10