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	$90.51	10.299%	$99.8316	$99.83	$99.85	$99.80
Purchase #2	$51.57	11.247%	$57.3701	$57.37	$57.35	$57.40
Purchase #3	$151.55	9.355%	$165.7275	$165.73	$165.75	$165.70
Purchase #4	$17.39	5.609%	$18.3654	$18.37	$18.35	$18.40
Purchase #5	$189.61	4.190%	$197.5547	$197.55	$197.55	$197.60
Purchase #6	$195.49	10.109%	$215.2521	$215.25	$215.25	$215.30
Purchase #7	$76.83	11.820%	$85.9113	$85.91	$85.90	$85.90
7 purchase totals =	$772.95		$840.0127	$840.01	$840.00	$840.10