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	$49.67	11.416%	$55.3403	$55.34	$55.35	$55.30
Purchase #2	$82.82	7.808%	$89.2866	$89.29	$89.30	$89.30
Purchase #3	$31.92	6.184%	$33.8939	$33.89	$33.90	$33.90
Purchase #4	$126.56	3.295%	$130.7302	$130.73	$130.75	$130.70
Purchase #5	$45.41	6.350%	$48.2935	$48.29	$48.30	$48.30
Purchase #6	$89.38	5.846%	$94.6052	$94.61	$94.60	$94.60
Purchase #7	$116.41	8.369%	$126.1524	$126.15	$126.15	$126.20
7 purchase totals =	$542.17		$578.3021	$578.30	$578.35	$578.30