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	$69.53	13.345%	$78.8088	$78.81	$78.80	$78.80
Purchase #2	$142.57	10.527%	$157.5783	$157.58	$157.60	$157.60
Purchase #3	$121.90	7.155%	$130.6219	$130.62	$130.60	$130.60
Purchase #4	$107.42	12.542%	$120.8926	$120.89	$120.90	$120.90
Purchase #5	$180.59	5.749%	$190.9721	$190.97	$190.95	$191.00
Purchase #6	$39.42	8.569%	$42.7979	$42.80	$42.80	$42.80
Purchase #7	$219.72	6.333%	$233.6349	$233.63	$233.65	$233.60
7 purchase totals =	$881.15		$955.3065	$955.30	$955.30	$955.30