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	$85.86	3.698%	$89.0351	$89.04	$89.05	$89.00
Purchase #2	$98.57	6.477%	$104.9544	$104.95	$104.95	$105.00
Purchase #3	$184.62	9.318%	$201.8229	$201.82	$201.80	$201.80
Purchase #4	$123.59	13.398%	$140.1486	$140.15	$140.15	$140.10
Purchase #5	$83.56	11.126%	$92.8569	$92.86	$92.85	$92.90
Purchase #6	$234.54	7.323%	$251.7154	$251.72	$251.70	$251.70
Purchase #7	$195.30	10.811%	$216.4139	$216.41	$216.40	$216.40
7 purchase totals =	$1,006.04		$1,096.9472	$1,096.95	$1,096.90	$1,096.90