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	$155.36	6.599%	$165.6122	$165.61	$165.60	$165.60
Purchase #2	$83.74	8.837%	$91.1401	$91.14	$91.15	$91.10
Purchase #3	$80.33	3.224%	$82.9198	$82.92	$82.90	$82.90
Purchase #4	$231.94	3.789%	$240.7282	$240.73	$240.75	$240.70
Purchase #5	$90.78	3.636%	$94.0808	$94.08	$94.10	$94.10
Purchase #6	$37.81	11.640%	$42.2111	$42.21	$42.20	$42.20
Purchase #7	$77.83	4.275%	$81.1572	$81.16	$81.15	$81.20
7 purchase totals =	$757.79		$797.8494	$797.85	$797.85	$797.80