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	$48.51	13.175%	$54.9012	$54.90	$54.90	$54.90
Purchase #2	$35.69	11.679%	$39.8582	$39.86	$39.85	$39.90
Purchase #3	$46.82	8.386%	$50.7463	$50.75	$50.75	$50.70
Purchase #4	$109.29	12.187%	$122.6092	$122.61	$122.60	$122.60
Purchase #5	$168.33	10.106%	$185.3414	$185.34	$185.35	$185.30
Purchase #6	$136.79	10.356%	$150.956	$150.96	$150.95	$151.00
Purchase #7	$81.88	4.543%	$85.5998	$85.60	$85.60	$85.60
7 purchase totals =	$627.31		$690.0121	$690.02	$690.00	$690.00