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	$149.81	7.120%	$160.4765	$160.48	$160.50	$160.50
Purchase #2	$235.65	6.224%	$250.3169	$250.32	$250.30	$250.30
Purchase #3	$85.30	10.453%	$94.2164	$94.22	$94.20	$94.20
Purchase #4	$71.76	8.794%	$78.0706	$78.07	$78.05	$78.10
Purchase #5	$91.69	8.196%	$99.2049	$99.20	$99.20	$99.20
Purchase #6	$14.54	6.670%	$15.5098	$15.51	$15.50	$15.50
Purchase #7	$76.38	12.666%	$86.0543	$86.05	$86.05	$86.10
7 purchase totals =	$725.13		$783.8494	$783.85	$783.80	$783.90