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	$142.51	10.260%	$157.1315	$157.13	$157.15	$157.10
Purchase #2	$20.48	5.352%	$21.5761	$21.58	$21.60	$21.60
Purchase #3	$91.57	7.516%	$98.4524	$98.45	$98.45	$98.50
Purchase #4	$53.43	13.123%	$60.4416	$60.44	$60.45	$60.40
Purchase #5	$55.64	7.514%	$59.8208	$59.82	$59.80	$59.80
Purchase #6	$27.88	9.450%	$30.5147	$30.51	$30.50	$30.50
Purchase #7	$144.26	10.834%	$159.8891	$159.89	$159.90	$159.90
7 purchase totals =	$535.77		$587.8262	$587.82	$587.85	$587.80