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	$165.56	13.570%	$188.0265	$188.03	$188.05	$188.00
Purchase #2	$221.61	7.626%	$238.51	$238.51	$238.50	$238.50
Purchase #3	$196.87	10.515%	$217.5709	$217.57	$217.55	$217.60
Purchase #4	$246.42	12.851%	$278.0874	$278.09	$278.10	$278.10
Purchase #5	$115.89	5.437%	$122.1909	$122.19	$122.20	$122.20
Purchase #6	$100.74	10.802%	$111.6219	$111.62	$111.60	$111.60
Purchase #7	$95.57	3.791%	$99.1931	$99.19	$99.20	$99.20
7 purchase totals =	$1,142.66		$1,255.2007	$1,255.20	$1,255.20	$1,255.20