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	$31.92	6.261%	$33.9185	$33.92	$33.90	$33.90
Purchase #2	$84.59	6.593%	$90.167	$90.17	$90.15	$90.20
Purchase #3	$64.32	5.574%	$67.9052	$67.91	$67.90	$67.90
Purchase #4	$169.43	3.692%	$175.6854	$175.69	$175.70	$175.70
Purchase #5	$101.38	4.160%	$105.5974	$105.60	$105.60	$105.60
Purchase #6	$50.97	3.721%	$52.8666	$52.87	$52.85	$52.90
Purchase #7	$33.84	5.133%	$35.577	$35.58	$35.60	$35.60
7 purchase totals =	$536.45		$561.7171	$561.74	$561.70	$561.80