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	$90.73	9.355%	$99.2178	$99.22	$99.20	$99.20
Purchase #2	$45.87	7.696%	$49.4002	$49.40	$49.40	$49.40
Purchase #3	$23.67	8.172%	$25.6043	$25.60	$25.60	$25.60
Purchase #4	$85.48	5.500%	$90.1814	$90.18	$90.20	$90.20
Purchase #5	$23.44	12.650%	$26.4052	$26.41	$26.40	$26.40
Purchase #6	$70.31	3.729%	$72.9319	$72.93	$72.95	$72.90
Purchase #7	$111.27	13.674%	$126.4851	$126.49	$126.50	$126.50
7 purchase totals =	$450.77		$490.2259	$490.23	$490.25	$490.20