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	$231.29	5.283%	$243.5091	$243.51	$243.50	$243.50
Purchase #2	$144.47	10.277%	$159.3172	$159.32	$159.30	$159.30
Purchase #3	$91.43	9.274%	$99.9092	$99.91	$99.90	$99.90
Purchase #4	$166.97	7.847%	$180.0721	$180.07	$180.05	$180.10
Purchase #5	$85.60	13.250%	$96.942	$96.94	$96.95	$96.90
Purchase #6	$100.46	10.367%	$110.8747	$110.87	$110.85	$110.90
Purchase #7	$123.34	6.353%	$131.1758	$131.18	$131.20	$131.20
7 purchase totals =	$943.56		$1,021.8001	$1,021.80	$1,021.75	$1,021.80