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	$17.37	7.153%	$18.6125	$18.61	$18.60	$18.60
Purchase #2	$32.36	8.869%	$35.23	$35.23	$35.25	$35.20
Purchase #3	$213.27	8.716%	$231.8586	$231.86	$231.85	$231.90
Purchase #4	$96.48	13.868%	$109.8598	$109.86	$109.85	$109.90
Purchase #5	$17.44	5.736%	$18.4404	$18.44	$18.45	$18.40
Purchase #6	$79.93	7.126%	$85.6258	$85.63	$85.65	$85.60
Purchase #7	$101.87	7.103%	$109.1058	$109.11	$109.10	$109.10
7 purchase totals =	$558.72		$608.7329	$608.74	$608.75	$608.70