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	$35.58	7.711%	$38.3236	$38.32	$38.30	$38.30
Purchase #2	$28.74	12.340%	$32.2865	$32.29	$32.30	$32.30
Purchase #3	$238.35	6.400%	$253.6044	$253.60	$253.60	$253.60
Purchase #4	$233.26	6.513%	$248.4522	$248.45	$248.45	$248.50
Purchase #5	$36.70	12.358%	$41.2354	$41.24	$41.25	$41.20
Purchase #6	$182.87	4.626%	$191.3296	$191.33	$191.35	$191.30
Purchase #7	$63.82	4.853%	$66.9172	$66.92	$66.90	$66.90
7 purchase totals =	$819.32		$872.1489	$872.15	$872.15	$872.10