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	$94.51	5.702%	$99.899	$99.90	$99.90	$99.90
Purchase #2	$55.76	7.189%	$59.7686	$59.77	$59.75	$59.80
Purchase #3	$167.70	6.253%	$178.1863	$178.19	$178.20	$178.20
Purchase #4	$229.33	4.150%	$238.8472	$238.85	$238.85	$238.80
Purchase #5	$58.87	4.589%	$61.5715	$61.57	$61.55	$61.60
Purchase #6	$19.88	8.222%	$21.5145	$21.51	$21.50	$21.50
Purchase #7	$144.83	7.541%	$155.7516	$155.75	$155.75	$155.80
7 purchase totals =	$770.88		$815.5387	$815.54	$815.50	$815.60