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	$126.75	11.324%	$141.1032	$141.10	$141.10	$141.10
Purchase #2	$152.79	6.524%	$162.758	$162.76	$162.75	$162.80
Purchase #3	$128.66	9.779%	$141.2417	$141.24	$141.25	$141.20
Purchase #4	$63.85	13.151%	$72.2469	$72.25	$72.25	$72.20
Purchase #5	$85.59	7.253%	$91.7978	$91.80	$91.80	$91.80
Purchase #6	$89.63	10.520%	$99.0591	$99.06	$99.05	$99.10
Purchase #7	$173.38	4.515%	$181.2081	$181.21	$181.20	$181.20
7 purchase totals =	$820.65		$889.4148	$889.42	$889.40	$889.40