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	$10.57	13.739%	$12.0222	$12.02	$12.00	$12.00
Purchase #2	$133.31	5.118%	$140.1328	$140.13	$140.15	$140.10
Purchase #3	$56.39	12.279%	$63.3141	$63.31	$63.30	$63.30
Purchase #4	$72.66	11.827%	$81.2535	$81.25	$81.25	$81.30
Purchase #5	$160.28	6.743%	$171.0877	$171.09	$171.10	$171.10
Purchase #6	$62.96	6.785%	$67.2318	$67.23	$67.25	$67.20
Purchase #7	$65.31	10.127%	$71.9239	$71.92	$71.90	$71.90
7 purchase totals =	$561.48		$606.9660	$606.95	$606.95	$606.90