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	$214.51	3.161%	$221.2907	$221.29	$221.30	$221.30
Purchase #2	$183.53	7.280%	$196.891	$196.89	$196.90	$196.90
Purchase #3	$214.27	8.845%	$233.2222	$233.22	$233.20	$233.20
Purchase #4	$65.75	9.318%	$71.8766	$71.88	$71.90	$71.90
Purchase #5	$9.53	7.310%	$10.2266	$10.23	$10.25	$10.20
Purchase #6	$7.87	9.705%	$8.6338	$8.63	$8.65	$8.60
Purchase #7	$210.82	8.751%	$229.2689	$229.27	$229.25	$229.30
7 purchase totals =	$906.28		$971.4098	$971.41	$971.45	$971.40