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	$47.53	6.539%	$50.638	$50.64	$50.65	$50.60
Purchase #2	$232.72	11.189%	$258.759	$258.76	$258.75	$258.80
Purchase #3	$106.85	13.804%	$121.5996	$121.60	$121.60	$121.60
Purchase #4	$67.54	7.589%	$72.6656	$72.67	$72.65	$72.70
Purchase #5	$124.29	4.653%	$130.0732	$130.07	$130.05	$130.10
Purchase #6	$99.56	5.595%	$105.1304	$105.13	$105.15	$105.10
Purchase #7	$119.49	10.371%	$131.8823	$131.88	$131.90	$131.90
7 purchase totals =	$797.98		$870.7481	$870.75	$870.75	$870.80