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	$113.89	8.282%	$123.3224	$123.32	$123.30	$123.30
Purchase #2	$151.66	12.829%	$171.1165	$171.12	$171.10	$171.10
Purchase #3	$128.40	7.859%	$138.491	$138.49	$138.50	$138.50
Purchase #4	$125.89	7.165%	$134.91	$134.91	$134.90	$134.90
Purchase #5	$40.67	4.871%	$42.651	$42.65	$42.65	$42.70
Purchase #6	$20.35	12.599%	$22.9139	$22.91	$22.90	$22.90
Purchase #7	$104.36	9.816%	$114.604	$114.60	$114.60	$114.60
7 purchase totals =	$685.22		$748.0088	$748.00	$747.95	$748.00