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	$88.75	10.335%	$97.9223	$97.92	$97.90	$97.90
Purchase #2	$166.47	10.629%	$184.1641	$184.16	$184.15	$184.20
Purchase #3	$87.47	4.542%	$91.4429	$91.44	$91.45	$91.40
Purchase #4	$61.90	3.602%	$64.1296	$64.13	$64.15	$64.10
Purchase #5	$82.89	7.648%	$89.2294	$89.23	$89.25	$89.20
Purchase #6	$105.49	13.272%	$119.4906	$119.49	$119.50	$119.50
Purchase #7	$130.83	6.115%	$138.8303	$138.83	$138.85	$138.80
7 purchase totals =	$723.80		$785.2092	$785.20	$785.25	$785.10