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	$69.87	3.579%	$72.3706	$72.37	$72.35	$72.40
Purchase #2	$203.89	12.756%	$229.8982	$229.90	$229.90	$229.90
Purchase #3	$12.98	4.560%	$13.5719	$13.57	$13.55	$13.60
Purchase #4	$211.65	6.449%	$225.2993	$225.30	$225.30	$225.30
Purchase #5	$88.34	3.199%	$91.166	$91.17	$91.15	$91.20
Purchase #6	$29.31	12.717%	$33.0374	$33.04	$33.05	$33.00
Purchase #7	$65.88	10.535%	$72.8205	$72.82	$72.80	$72.80
7 purchase totals =	$681.92		$738.1639	$738.17	$738.10	$738.20