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	$49.27	3.111%	$50.8028	$50.80	$50.80	$50.80
Purchase #2	$123.57	3.361%	$127.7232	$127.72	$127.70	$127.70
Purchase #3	$215.33	12.873%	$243.0494	$243.05	$243.05	$243.00
Purchase #4	$52.80	12.429%	$59.3625	$59.36	$59.35	$59.40
Purchase #5	$106.68	10.178%	$117.5379	$117.54	$117.55	$117.50
Purchase #6	$177.85	12.419%	$199.9372	$199.94	$199.95	$199.90
Purchase #7	$136.86	3.759%	$142.0046	$142.00	$142.00	$142.00
7 purchase totals =	$862.36		$940.4176	$940.41	$940.40	$940.30