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	$242.54	12.628%	$273.168	$273.17	$273.15	$273.20
Purchase #2	$48.37	8.758%	$52.6062	$52.61	$52.60	$52.60
Purchase #3	$45.56	11.199%	$50.6623	$50.66	$50.65	$50.70
Purchase #4	$118.98	7.801%	$128.2616	$128.26	$128.25	$128.30
Purchase #5	$234.35	4.172%	$244.1271	$244.13	$244.15	$244.10
Purchase #6	$200.33	10.832%	$222.0297	$222.03	$222.05	$222.00
Purchase #7	$153.93	9.821%	$169.0475	$169.05	$169.05	$169.00
7 purchase totals =	$1,044.06		$1,139.9024	$1,139.91	$1,139.90	$1,139.90