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	$7.68	9.279%	$8.3926	$8.39	$8.40	$8.40
Purchase #2	$101.56	8.485%	$110.1774	$110.18	$110.20	$110.20
Purchase #3	$37.63	10.141%	$41.4461	$41.45	$41.45	$41.40
Purchase #4	$47.50	12.808%	$53.5838	$53.58	$53.60	$53.60
Purchase #5	$237.46	9.443%	$259.8833	$259.88	$259.90	$259.90
Purchase #6	$68.94	13.740%	$78.4124	$78.41	$78.40	$78.40
Purchase #7	$52.51	9.478%	$57.4869	$57.49	$57.50	$57.50
7 purchase totals =	$553.28		$609.3825	$609.38	$609.45	$609.40