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	$192.72	11.847%	$215.5515	$215.55	$215.55	$215.60
Purchase #2	$67.37	8.709%	$73.2373	$73.24	$73.25	$73.20
Purchase #3	$40.68	7.424%	$43.7001	$43.70	$43.70	$43.70
Purchase #4	$61.59	6.492%	$65.5884	$65.59	$65.60	$65.60
Purchase #5	$52.67	13.212%	$59.6288	$59.63	$59.65	$59.60
Purchase #6	$127.73	6.786%	$136.3978	$136.40	$136.40	$136.40
Purchase #7	$41.34	7.582%	$44.4744	$44.47	$44.45	$44.50
7 purchase totals =	$584.10		$638.5783	$638.58	$638.60	$638.60