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	$18.80	9.563%	$20.5978	$20.60	$20.60	$20.60
Purchase #2	$143.65	11.539%	$160.2258	$160.23	$160.25	$160.20
Purchase #3	$167.87	10.551%	$185.582	$185.58	$185.60	$185.60
Purchase #4	$79.69	7.426%	$85.6078	$85.61	$85.60	$85.60
Purchase #5	$35.27	10.443%	$38.9532	$38.95	$38.95	$39.00
Purchase #6	$225.34	4.150%	$234.6916	$234.69	$234.70	$234.70
Purchase #7	$75.82	7.239%	$81.3086	$81.31	$81.30	$81.30
7 purchase totals =	$746.44		$806.9668	$806.97	$807.00	$807.00