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	$93.60	6.588%	$99.7664	$99.77	$99.75	$99.80
Purchase #2	$95.37	8.643%	$103.6128	$103.61	$103.60	$103.60
Purchase #3	$219.35	8.836%	$238.7318	$238.73	$238.75	$238.70
Purchase #4	$96.88	4.541%	$101.2793	$101.28	$101.30	$101.30
Purchase #5	$36.34	12.446%	$40.8629	$40.86	$40.85	$40.90
Purchase #6	$207.58	7.331%	$222.7977	$222.80	$222.80	$222.80
Purchase #7	$161.60	8.339%	$175.0758	$175.08	$175.10	$175.10
7 purchase totals =	$910.72		$982.1267	$982.13	$982.15	$982.20