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	$28.95	11.386%	$32.2462	$32.25	$32.25	$32.20
Purchase #2	$144.61	9.668%	$158.5909	$158.59	$158.60	$158.60
Purchase #3	$57.51	6.659%	$61.3396	$61.34	$61.35	$61.30
Purchase #4	$129.40	11.703%	$144.5437	$144.54	$144.55	$144.50
Purchase #5	$65.90	13.270%	$74.6449	$74.64	$74.65	$74.60
Purchase #6	$83.33	10.121%	$91.7638	$91.76	$91.75	$91.80
Purchase #7	$178.90	4.114%	$186.2599	$186.26	$186.25	$186.30
7 purchase totals =	$688.60		$749.3890	$749.38	$749.40	$749.30