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	$122.44	6.820%	$130.7904	$130.79	$130.80	$130.80
Purchase #2	$39.86	8.161%	$43.113	$43.11	$43.10	$43.10
Purchase #3	$187.64	4.212%	$195.5434	$195.54	$195.55	$195.50
Purchase #4	$197.88	12.442%	$222.5002	$222.50	$222.50	$222.50
Purchase #5	$155.98	11.365%	$173.7071	$173.71	$173.70	$173.70
Purchase #6	$63.90	11.260%	$71.0951	$71.10	$71.10	$71.10
Purchase #7	$93.97	7.196%	$100.7321	$100.73	$100.75	$100.70
7 purchase totals =	$861.67		$937.4813	$937.48	$937.50	$937.40