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	$107.35	4.240%	$111.9016	$111.90	$111.90	$111.90
Purchase #2	$124.74	3.365%	$128.9375	$128.94	$128.95	$128.90
Purchase #3	$243.31	8.566%	$264.1519	$264.15	$264.15	$264.20
Purchase #4	$91.61	13.114%	$103.6237	$103.62	$103.60	$103.60
Purchase #5	$98.87	3.363%	$102.195	$102.20	$102.20	$102.20
Purchase #6	$131.53	10.659%	$145.5498	$145.55	$145.55	$145.50
Purchase #7	$131.43	7.426%	$141.19	$141.19	$141.20	$141.20
7 purchase totals =	$928.84		$997.5495	$997.55	$997.55	$997.50