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	$18.95	5.791%	$20.0474	$20.05	$20.05	$20.00
Purchase #2	$137.28	13.579%	$155.9213	$155.92	$155.90	$155.90
Purchase #3	$114.28	7.655%	$123.0281	$123.03	$123.05	$123.00
Purchase #4	$30.36	8.821%	$33.0381	$33.04	$33.05	$33.00
Purchase #5	$193.26	8.833%	$210.3307	$210.33	$210.35	$210.30
Purchase #6	$95.25	4.688%	$99.7153	$99.72	$99.70	$99.70
Purchase #7	$140.53	7.748%	$151.4183	$151.42	$151.40	$151.40
7 purchase totals =	$729.91		$793.4992	$793.51	$793.50	$793.30