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	$78.46	3.867%	$81.494	$81.49	$81.50	$81.50
Purchase #2	$36.65	11.641%	$40.9164	$40.92	$40.90	$40.90
Purchase #3	$162.39	9.706%	$178.1516	$178.15	$178.15	$178.20
Purchase #4	$92.72	13.313%	$105.0638	$105.06	$105.05	$105.10
Purchase #5	$121.72	8.292%	$131.813	$131.81	$131.80	$131.80
Purchase #6	$80.89	3.674%	$83.8619	$83.86	$83.85	$83.90
Purchase #7	$71.90	10.571%	$79.5005	$79.50	$79.50	$79.50
7 purchase totals =	$644.73		$700.8012	$700.79	$700.75	$700.90