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	$48.48	4.384%	$50.6054	$50.61	$50.60	$50.60
Purchase #2	$157.50	10.582%	$174.1667	$174.17	$174.15	$174.20
Purchase #3	$59.54	13.874%	$67.8006	$67.80	$67.80	$67.80
Purchase #4	$211.63	10.249%	$233.32	$233.32	$233.30	$233.30
Purchase #5	$145.94	5.449%	$153.8923	$153.89	$153.90	$153.90
Purchase #6	$22.55	11.445%	$25.1308	$25.13	$25.15	$25.10
Purchase #7	$134.95	11.580%	$150.5772	$150.58	$150.60	$150.60
7 purchase totals =	$780.59		$855.4930	$855.50	$855.50	$855.50