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	$18.34	9.735%	$20.1254	$20.13	$20.15	$20.10
Purchase #2	$133.89	10.822%	$148.3796	$148.38	$148.40	$148.40
Purchase #3	$52.59	8.104%	$56.8519	$56.85	$56.85	$56.90
Purchase #4	$50.60	11.542%	$56.4403	$56.44	$56.45	$56.40
Purchase #5	$14.48	4.785%	$15.1729	$15.17	$15.15	$15.20
Purchase #6	$151.45	9.112%	$165.2501	$165.25	$165.25	$165.30
Purchase #7	$187.98	4.118%	$195.721	$195.72	$195.70	$195.70
7 purchase totals =	$609.33		$657.9412	$657.94	$657.95	$658.00