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	$40.78	3.584%	$42.2416	$42.24	$42.25	$42.20
Purchase #2	$146.84	7.692%	$158.1349	$158.13	$158.15	$158.10
Purchase #3	$86.67	7.223%	$92.9302	$92.93	$92.95	$92.90
Purchase #4	$222.76	12.245%	$250.037	$250.04	$250.05	$250.00
Purchase #5	$136.50	7.326%	$146.5	$146.50	$146.50	$146.50
Purchase #6	$29.38	11.505%	$32.7602	$32.76	$32.75	$32.80
Purchase #7	$212.55	7.690%	$228.8951	$228.90	$228.90	$228.90
7 purchase totals =	$875.48		$951.4990	$951.50	$951.55	$951.40