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	$111.87	11.256%	$124.4621	$124.46	$124.45	$124.50
Purchase #2	$99.27	9.640%	$108.8396	$108.84	$108.85	$108.80
Purchase #3	$101.77	9.503%	$111.4412	$111.44	$111.45	$111.40
Purchase #4	$230.65	4.224%	$240.3927	$240.39	$240.40	$240.40
Purchase #5	$41.61	9.724%	$45.6562	$45.66	$45.65	$45.70
Purchase #6	$250.94	5.293%	$264.2223	$264.22	$264.20	$264.20
Purchase #7	$57.64	8.119%	$62.3198	$62.32	$62.30	$62.30
7 purchase totals =	$893.75		$957.3339	$957.33	$957.30	$957.30