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	$51.74	4.767%	$54.2064	$54.21	$54.20	$54.20
Purchase #2	$227.46	12.229%	$255.2761	$255.28	$255.30	$255.30
Purchase #3	$91.59	7.356%	$98.3274	$98.33	$98.35	$98.30
Purchase #4	$152.57	4.581%	$159.5592	$159.56	$159.55	$159.60
Purchase #5	$45.83	10.874%	$50.8136	$50.81	$50.80	$50.80
Purchase #6	$178.71	10.307%	$197.1296	$197.13	$197.15	$197.10
Purchase #7	$43.49	5.426%	$45.8498	$45.85	$45.85	$45.80
7 purchase totals =	$791.39		$861.1621	$861.17	$861.20	$861.10