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	$11.45	6.841%	$12.2333	$12.23	$12.25	$12.20
Purchase #2	$84.45	7.327%	$90.6377	$90.64	$90.65	$90.60
Purchase #3	$37.85	3.620%	$39.2202	$39.22	$39.20	$39.20
Purchase #4	$206.89	12.571%	$232.8981	$232.90	$232.90	$232.90
Purchase #5	$79.73	4.139%	$83.03	$83.03	$83.05	$83.00
Purchase #6	$89.96	12.254%	$100.9837	$100.98	$101.00	$101.00
Purchase #7	$121.59	5.561%	$128.3516	$128.35	$128.35	$128.40
7 purchase totals =	$631.92		$687.3546	$687.35	$687.40	$687.30