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	$34.79	7.794%	$37.5015	$37.50	$37.50	$37.50
Purchase #2	$156.60	8.135%	$169.3394	$169.34	$169.35	$169.30
Purchase #3	$102.55	13.634%	$116.5317	$116.53	$116.55	$116.50
Purchase #4	$96.44	12.474%	$108.4699	$108.47	$108.45	$108.50
Purchase #5	$27.45	6.261%	$29.1686	$29.17	$29.15	$29.20
Purchase #6	$248.63	6.404%	$264.5523	$264.55	$264.55	$264.60
Purchase #7	$180.84	5.795%	$191.3197	$191.32	$191.30	$191.30
7 purchase totals =	$847.30		$916.8831	$916.88	$916.85	$916.90