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	$53.41	12.260%	$59.9581	$59.96	$59.95	$60.00
Purchase #2	$160.33	6.381%	$170.5607	$170.56	$170.55	$170.60
Purchase #3	$203.42	3.389%	$210.3139	$210.31	$210.30	$210.30
Purchase #4	$43.37	10.164%	$47.7781	$47.78	$47.80	$47.80
Purchase #5	$123.90	11.457%	$138.0952	$138.10	$138.10	$138.10
Purchase #6	$231.84	3.160%	$239.1661	$239.17	$239.15	$239.20
Purchase #7	$199.27	10.130%	$219.4561	$219.46	$219.45	$219.50
7 purchase totals =	$1,015.54		$1,085.3282	$1,085.34	$1,085.30	$1,085.50