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	$18.47	10.528%	$20.4145	$20.41	$20.40	$20.40
Purchase #2	$234.89	13.205%	$265.9072	$265.91	$265.90	$265.90
Purchase #3	$9.40	6.118%	$9.9751	$9.98	$10.00	$10.00
Purchase #4	$42.77	7.251%	$45.8713	$45.87	$45.85	$45.90
Purchase #5	$59.84	11.712%	$66.8485	$66.85	$66.85	$66.80
Purchase #6	$189.57	8.361%	$205.4199	$205.42	$205.40	$205.40
Purchase #7	$136.61	8.175%	$147.7779	$147.78	$147.80	$147.80
7 purchase totals =	$691.55		$762.2144	$762.22	$762.20	$762.20