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	$130.94	13.538%	$148.6667	$148.67	$148.65	$148.70
Purchase #2	$54.87	4.874%	$57.5444	$57.54	$57.55	$57.50
Purchase #3	$169.49	7.226%	$181.7373	$181.74	$181.75	$181.70
Purchase #4	$218.76	5.723%	$231.2796	$231.28	$231.30	$231.30
Purchase #5	$54.68	11.844%	$61.1563	$61.16	$61.15	$61.20
Purchase #6	$85.52	6.819%	$91.3516	$91.35	$91.35	$91.40
Purchase #7	$59.79	12.835%	$67.464	$67.46	$67.45	$67.50
7 purchase totals =	$774.05		$839.1999	$839.20	$839.20	$839.30