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	$42.36	10.324%	$46.7332	$46.73	$46.75	$46.70
Purchase #2	$99.38	12.390%	$111.6932	$111.69	$111.70	$111.70
Purchase #3	$39.63	10.507%	$43.7939	$43.79	$43.80	$43.80
Purchase #4	$108.89	8.377%	$118.0117	$118.01	$118.00	$118.00
Purchase #5	$141.74	3.570%	$146.8001	$146.80	$146.80	$146.80
Purchase #6	$85.93	6.286%	$91.3316	$91.33	$91.35	$91.30
Purchase #7	$161.74	6.268%	$171.8779	$171.88	$171.90	$171.90
7 purchase totals =	$679.67		$730.2416	$730.23	$730.30	$730.20