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	$81.42	12.117%	$91.2857	$91.29	$91.30	$91.30
Purchase #2	$249.51	6.333%	$265.3115	$265.31	$265.30	$265.30
Purchase #3	$165.91	13.765%	$188.7475	$188.75	$188.75	$188.70
Purchase #4	$154.33	4.573%	$161.3875	$161.39	$161.40	$161.40
Purchase #5	$94.63	7.279%	$101.5181	$101.52	$101.50	$101.50
Purchase #6	$145.60	12.671%	$164.049	$164.05	$164.05	$164.00
Purchase #7	$115.71	10.664%	$128.0493	$128.05	$128.05	$128.00
7 purchase totals =	$1,007.11		$1,100.3486	$1,100.36	$1,100.35	$1,100.20