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	$34.51	7.582%	$37.1265	$37.13	$37.15	$37.10
Purchase #2	$129.90	11.153%	$144.3877	$144.39	$144.40	$144.40
Purchase #3	$144.89	4.609%	$151.568	$151.57	$151.55	$151.60
Purchase #4	$83.31	9.374%	$91.1195	$91.12	$91.10	$91.10
Purchase #5	$29.98	13.564%	$34.0465	$34.05	$34.05	$34.00
Purchase #6	$187.33	13.433%	$212.494	$212.49	$212.50	$212.50
Purchase #7	$165.51	12.551%	$186.2832	$186.28	$186.30	$186.30
7 purchase totals =	$775.43		$857.0254	$857.03	$857.05	$857.00