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	$16.43	13.239%	$18.6052	$18.61	$18.60	$18.60
Purchase #2	$245.56	12.320%	$275.813	$275.81	$275.80	$275.80
Purchase #3	$161.74	4.843%	$169.5731	$169.57	$169.55	$169.60
Purchase #4	$188.48	7.286%	$202.2127	$202.21	$202.20	$202.20
Purchase #5	$144.94	4.769%	$151.8522	$151.85	$151.85	$151.90
Purchase #6	$130.46	13.382%	$147.9182	$147.92	$147.90	$147.90
Purchase #7	$57.42	3.440%	$59.3952	$59.40	$59.40	$59.40
7 purchase totals =	$945.03		$1,025.3696	$1,025.37	$1,025.30	$1,025.40