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	$133.54	6.440%	$142.14	$142.14	$142.15	$142.10
Purchase #2	$102.41	6.576%	$109.1445	$109.14	$109.15	$109.10
Purchase #3	$25.66	13.420%	$29.1036	$29.10	$29.10	$29.10
Purchase #4	$76.45	11.634%	$85.3442	$85.34	$85.35	$85.30
Purchase #5	$64.26	11.829%	$71.8613	$71.86	$71.85	$71.90
Purchase #6	$218.62	12.237%	$245.3725	$245.37	$245.35	$245.40
Purchase #7	$35.45	5.267%	$37.3172	$37.32	$37.30	$37.30
7 purchase totals =	$656.39		$720.2833	$720.27	$720.25	$720.20