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	$19.64	13.236%	$22.2396	$22.24	$22.25	$22.20
Purchase #2	$153.65	11.512%	$171.3382	$171.34	$171.35	$171.30
Purchase #3	$46.51	8.108%	$50.281	$50.28	$50.30	$50.30
Purchase #4	$148.59	10.516%	$164.2157	$164.22	$164.20	$164.20
Purchase #5	$36.39	11.163%	$40.4522	$40.45	$40.45	$40.50
Purchase #6	$24.73	8.830%	$26.9137	$26.91	$26.90	$26.90
Purchase #7	$125.39	13.656%	$142.5133	$142.51	$142.50	$142.50
7 purchase totals =	$554.90		$617.9537	$617.95	$617.95	$617.90