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	$9.98	5.460%	$10.5249	$10.52	$10.50	$10.50
Purchase #2	$125.37	6.490%	$133.5065	$133.51	$133.50	$133.50
Purchase #3	$140.30	9.257%	$153.2876	$153.29	$153.30	$153.30
Purchase #4	$249.31	13.333%	$282.5505	$282.55	$282.55	$282.60
Purchase #5	$93.82	4.342%	$97.8937	$97.89	$97.90	$97.90
Purchase #6	$45.35	11.411%	$50.5249	$50.52	$50.50	$50.50
Purchase #7	$55.74	12.820%	$62.8859	$62.89	$62.90	$62.90
7 purchase totals =	$719.87		$791.1740	$791.17	$791.15	$791.20