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	$52.56	12.793%	$59.284	$59.28	$59.30	$59.30
Purchase #2	$239.95	7.512%	$257.975	$257.98	$258.00	$258.00
Purchase #3	$96.32	13.406%	$109.2327	$109.23	$109.25	$109.20
Purchase #4	$23.69	11.741%	$26.4714	$26.47	$26.45	$26.50
Purchase #5	$91.32	8.646%	$99.2155	$99.22	$99.20	$99.20
Purchase #6	$48.89	13.123%	$55.3058	$55.31	$55.30	$55.30
Purchase #7	$206.95	10.251%	$228.1644	$228.16	$228.15	$228.20
7 purchase totals =	$759.68		$835.6488	$835.65	$835.65	$835.70