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	$158.47	13.439%	$179.7668	$179.77	$179.75	$179.80
Purchase #2	$102.76	9.306%	$112.3228	$112.32	$112.30	$112.30
Purchase #3	$152.39	4.250%	$158.8666	$158.87	$158.85	$158.90
Purchase #4	$82.69	9.669%	$90.6853	$90.69	$90.70	$90.70
Purchase #5	$28.89	3.740%	$29.9705	$29.97	$29.95	$30.00
Purchase #6	$126.33	4.140%	$131.5601	$131.56	$131.55	$131.60
Purchase #7	$233.48	13.499%	$264.9975	$265.00	$265.00	$265.00
7 purchase totals =	$885.01		$968.1696	$968.18	$968.10	$968.30