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	$237.28	5.285%	$249.8202	$249.82	$249.80	$249.80
Purchase #2	$32.64	5.743%	$34.5145	$34.51	$34.50	$34.50
Purchase #3	$61.78	9.712%	$67.7801	$67.78	$67.80	$67.80
Purchase #4	$159.33	8.320%	$172.5863	$172.59	$172.60	$172.60
Purchase #5	$123.31	6.237%	$131.0008	$131.00	$131.00	$131.00
Purchase #6	$92.84	6.592%	$98.96	$98.96	$98.95	$99.00
Purchase #7	$165.30	3.192%	$170.5764	$170.58	$170.60	$170.60
7 purchase totals =	$872.48		$925.2383	$925.24	$925.25	$925.30