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	$249.98	13.774%	$284.4122	$284.41	$284.40	$284.40
Purchase #2	$142.98	6.486%	$152.2537	$152.25	$152.25	$152.30
Purchase #3	$26.36	12.435%	$29.6379	$29.64	$29.65	$29.60
Purchase #4	$33.89	13.331%	$38.4079	$38.41	$38.40	$38.40
Purchase #5	$124.87	9.523%	$136.7614	$136.76	$136.75	$136.80
Purchase #6	$35.48	5.447%	$37.4126	$37.41	$37.40	$37.40
Purchase #7	$131.36	8.559%	$142.6031	$142.60	$142.60	$142.60
7 purchase totals =	$744.92		$821.4888	$821.48	$821.45	$821.50