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	$192.61	4.286%	$200.8653	$200.87	$200.85	$200.90
Purchase #2	$123.73	12.729%	$139.4796	$139.48	$139.50	$139.50
Purchase #3	$224.47	9.488%	$245.7677	$245.77	$245.75	$245.80
Purchase #4	$217.42	11.367%	$242.1341	$242.13	$242.15	$242.10
Purchase #5	$249.52	11.539%	$278.3121	$278.31	$278.30	$278.30
Purchase #6	$147.94	10.778%	$163.885	$163.89	$163.90	$163.90
Purchase #7	$126.63	12.443%	$142.3866	$142.39	$142.40	$142.40
7 purchase totals =	$1,282.32		$1,412.8304	$1,412.84	$1,412.85	$1,412.90