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	$53.69	6.309%	$57.0773	$57.08	$57.10	$57.10
Purchase #2	$74.64	5.654%	$78.8601	$78.86	$78.85	$78.90
Purchase #3	$138.33	10.556%	$152.9321	$152.93	$152.95	$152.90
Purchase #4	$242.34	11.363%	$269.8771	$269.88	$269.90	$269.90
Purchase #5	$134.64	12.264%	$151.1522	$151.15	$151.15	$151.20
Purchase #6	$32.45	3.834%	$33.6941	$33.69	$33.70	$33.70
Purchase #7	$127.64	12.855%	$144.0481	$144.05	$144.05	$144.00
7 purchase totals =	$803.73		$887.6410	$887.64	$887.70	$887.70