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	$111.30	8.170%	$120.3932	$120.39	$120.40	$120.40
Purchase #2	$180.57	4.735%	$189.12	$189.12	$189.10	$189.10
Purchase #3	$136.49	4.612%	$142.7849	$142.78	$142.80	$142.80
Purchase #4	$92.35	10.747%	$102.2749	$102.27	$102.25	$102.30
Purchase #5	$249.35	9.434%	$272.8737	$272.87	$272.85	$272.90
Purchase #6	$243.77	8.520%	$264.5392	$264.54	$264.55	$264.50
Purchase #7	$6.59	6.637%	$7.0274	$7.03	$7.05	$7.00
7 purchase totals =	$1,020.42		$1,099.0133	$1,099.00	$1,099.00	$1,099.00