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	$37.68	13.760%	$42.8648	$42.86	$42.85	$42.90
Purchase #2	$20.60	9.169%	$22.4888	$22.49	$22.50	$22.50
Purchase #3	$189.56	11.679%	$211.6987	$211.70	$211.70	$211.70
Purchase #4	$222.76	3.640%	$230.8685	$230.87	$230.85	$230.90
Purchase #5	$82.60	10.806%	$91.5258	$91.53	$91.55	$91.50
Purchase #6	$203.32	10.516%	$224.7011	$224.70	$224.70	$224.70
Purchase #7	$187.79	4.850%	$196.8978	$196.90	$196.90	$196.90
7 purchase totals =	$944.31		$1,021.0455	$1,021.05	$1,021.05	$1,021.10