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	$109.83	8.701%	$119.3863	$119.39	$119.40	$119.40
Purchase #2	$158.51	12.217%	$177.8752	$177.88	$177.90	$177.90
Purchase #3	$239.35	4.752%	$250.7239	$250.72	$250.70	$250.70
Purchase #4	$146.98	12.594%	$165.4907	$165.49	$165.50	$165.50
Purchase #5	$141.39	10.620%	$156.4056	$156.41	$156.40	$156.40
Purchase #6	$241.77	5.789%	$255.7661	$255.77	$255.75	$255.80
Purchase #7	$141.90	7.591%	$152.6716	$152.67	$152.65	$152.70
7 purchase totals =	$1,179.73		$1,278.3194	$1,278.33	$1,278.30	$1,278.40