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	$38.35	10.209%	$42.2652	$42.27	$42.25	$42.30
Purchase #2	$131.59	11.703%	$146.99	$146.99	$147.00	$147.00
Purchase #3	$91.79	8.109%	$99.2333	$99.23	$99.25	$99.20
Purchase #4	$63.82	13.391%	$72.3661	$72.37	$72.35	$72.40
Purchase #5	$17.41	3.703%	$18.0547	$18.05	$18.05	$18.10
Purchase #6	$92.36	10.737%	$102.2767	$102.28	$102.30	$102.30
Purchase #7	$120.25	9.825%	$132.0646	$132.06	$132.05	$132.10
7 purchase totals =	$555.57		$613.2506	$613.25	$613.25	$613.40