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	$67.79	6.408%	$72.134	$72.13	$72.15	$72.10
Purchase #2	$242.69	5.782%	$256.7223	$256.72	$256.70	$256.70
Purchase #3	$122.84	10.761%	$136.0588	$136.06	$136.05	$136.10
Purchase #4	$195.89	13.629%	$222.5878	$222.59	$222.60	$222.60
Purchase #5	$174.25	11.597%	$194.4578	$194.46	$194.45	$194.50
Purchase #6	$153.71	11.655%	$171.6249	$171.62	$171.60	$171.60
Purchase #7	$177.67	12.668%	$200.1772	$200.18	$200.20	$200.20
7 purchase totals =	$1,134.84		$1,253.7628	$1,253.76	$1,253.75	$1,253.80