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	$36.39	3.268%	$37.5792	$37.58	$37.60	$37.60
Purchase #2	$175.66	13.236%	$198.9104	$198.91	$198.90	$198.90
Purchase #3	$57.45	10.570%	$63.5225	$63.52	$63.50	$63.50
Purchase #4	$30.96	4.132%	$32.2393	$32.24	$32.25	$32.20
Purchase #5	$109.84	12.699%	$123.7886	$123.79	$123.80	$123.80
Purchase #6	$68.63	4.648%	$71.8199	$71.82	$71.80	$71.80
Purchase #7	$148.43	12.821%	$167.4602	$167.46	$167.45	$167.50
7 purchase totals =	$627.36		$695.3201	$695.32	$695.30	$695.30