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	$84.56	9.476%	$92.5729	$92.57	$92.55	$92.60
Purchase #2	$86.93	10.327%	$95.9073	$95.91	$95.90	$95.90
Purchase #3	$57.95	6.454%	$61.6901	$61.69	$61.70	$61.70
Purchase #4	$148.47	9.705%	$162.879	$162.88	$162.90	$162.90
Purchase #5	$111.60	5.752%	$118.0192	$118.02	$118.00	$118.00
Purchase #6	$42.40	6.394%	$45.1111	$45.11	$45.10	$45.10
Purchase #7	$250.72	4.626%	$262.3183	$262.32	$262.30	$262.30
7 purchase totals =	$782.63		$838.4979	$838.50	$838.45	$838.50