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	$175.25	8.352%	$189.8869	$189.89	$189.90	$189.90
Purchase #2	$153.83	7.363%	$165.1565	$165.16	$165.15	$165.20
Purchase #3	$39.66	6.448%	$42.2173	$42.22	$42.20	$42.20
Purchase #4	$154.81	9.721%	$169.8591	$169.86	$169.85	$169.90
Purchase #5	$16.52	9.346%	$18.064	$18.06	$18.05	$18.10
Purchase #6	$34.86	9.330%	$38.1124	$38.11	$38.10	$38.10
Purchase #7	$197.40	6.159%	$209.5579	$209.56	$209.55	$209.60
7 purchase totals =	$772.33		$832.8541	$832.86	$832.80	$833.00