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	$65.92	11.535%	$73.5239	$73.52	$73.50	$73.50
Purchase #2	$148.61	7.824%	$160.2372	$160.24	$160.25	$160.20
Purchase #3	$24.26	3.471%	$25.1021	$25.10	$25.10	$25.10
Purchase #4	$32.97	13.473%	$37.412	$37.41	$37.40	$37.40
Purchase #5	$6.87	12.510%	$7.7294	$7.73	$7.75	$7.70
Purchase #6	$88.95	13.447%	$100.9111	$100.91	$100.90	$100.90
Purchase #7	$123.82	3.441%	$128.0806	$128.08	$128.10	$128.10
7 purchase totals =	$491.40		$532.9963	$532.99	$533.00	$532.90