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	$82.79	8.286%	$89.65	$89.65	$89.65	$89.70
Purchase #2	$36.84	3.297%	$38.0546	$38.05	$38.05	$38.10
Purchase #3	$103.38	5.307%	$108.8664	$108.87	$108.85	$108.90
Purchase #4	$54.87	12.209%	$61.5691	$61.57	$61.55	$61.60
Purchase #5	$80.55	13.166%	$91.1552	$91.16	$91.15	$91.20
Purchase #6	$34.48	7.872%	$37.1943	$37.19	$37.20	$37.20
Purchase #7	$71.72	12.473%	$80.6656	$80.67	$80.65	$80.70
7 purchase totals =	$464.63		$507.1552	$507.16	$507.10	$507.40