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	$109.38	9.766%	$120.0621	$120.06	$120.05	$120.10
Purchase #2	$212.83	7.639%	$229.0881	$229.09	$229.10	$229.10
Purchase #3	$115.46	11.440%	$128.6686	$128.67	$128.65	$128.70
Purchase #4	$242.85	9.216%	$265.2311	$265.23	$265.25	$265.20
Purchase #5	$81.46	4.619%	$85.2226	$85.22	$85.20	$85.20
Purchase #6	$105.75	3.631%	$109.5898	$109.59	$109.60	$109.60
Purchase #7	$88.40	4.565%	$92.4355	$92.44	$92.45	$92.40
7 purchase totals =	$956.13		$1,030.2978	$1,030.30	$1,030.30	$1,030.30