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	$76.84	6.395%	$81.7539	$81.75	$81.75	$81.80
Purchase #2	$75.93	9.283%	$82.9786	$82.98	$83.00	$83.00
Purchase #3	$147.83	3.819%	$153.4756	$153.48	$153.50	$153.50
Purchase #4	$118.81	4.276%	$123.8903	$123.89	$123.90	$123.90
Purchase #5	$104.26	6.764%	$111.3121	$111.31	$111.30	$111.30
Purchase #6	$40.42	13.457%	$45.8593	$45.86	$45.85	$45.90
Purchase #7	$52.74	11.788%	$58.957	$58.96	$58.95	$59.00
7 purchase totals =	$616.83		$658.2268	$658.23	$658.25	$658.40