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	$16.97	9.833%	$18.6387	$18.64	$18.65	$18.60
Purchase #2	$89.72	12.226%	$100.6892	$100.69	$100.70	$100.70
Purchase #3	$6.44	9.869%	$7.0756	$7.08	$7.10	$7.10
Purchase #4	$45.68	12.213%	$51.2589	$51.26	$51.25	$51.30
Purchase #5	$194.51	10.478%	$214.8908	$214.89	$214.90	$214.90
Purchase #6	$223.30	6.591%	$238.0177	$238.02	$238.00	$238.00
Purchase #7	$106.31	3.767%	$110.3147	$110.31	$110.30	$110.30
7 purchase totals =	$682.93		$740.8856	$740.89	$740.90	$740.90