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	$60.82	11.665%	$67.9147	$67.91	$67.90	$67.90
Purchase #2	$28.34	10.310%	$31.2619	$31.26	$31.25	$31.30
Purchase #3	$106.79	9.851%	$117.3099	$117.31	$117.30	$117.30
Purchase #4	$157.63	10.492%	$174.1685	$174.17	$174.15	$174.20
Purchase #5	$64.92	12.335%	$72.9279	$72.93	$72.95	$72.90
Purchase #6	$44.72	5.641%	$47.2427	$47.24	$47.25	$47.20
Purchase #7	$75.58	7.821%	$81.4911	$81.49	$81.50	$81.50
7 purchase totals =	$538.80		$592.3167	$592.31	$592.30	$592.30