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	$32.47	11.736%	$36.2807	$36.28	$36.30	$36.30
Purchase #2	$176.40	8.812%	$191.9444	$191.94	$191.95	$191.90
Purchase #3	$248.55	10.384%	$274.3594	$274.36	$274.35	$274.40
Purchase #4	$26.73	8.124%	$28.9015	$28.90	$28.90	$28.90
Purchase #5	$57.76	12.147%	$64.7761	$64.78	$64.80	$64.80
Purchase #6	$153.92	8.139%	$166.4475	$166.45	$166.45	$166.40
Purchase #7	$151.95	11.125%	$168.8544	$168.85	$168.85	$168.90
7 purchase totals =	$847.78		$931.5640	$931.56	$931.60	$931.60