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	$109.57	5.714%	$115.8308	$115.83	$115.85	$115.80
Purchase #2	$82.37	8.215%	$89.1367	$89.14	$89.15	$89.10
Purchase #3	$158.79	13.617%	$180.4124	$180.41	$180.40	$180.40
Purchase #4	$92.55	7.465%	$99.4589	$99.46	$99.45	$99.50
Purchase #5	$170.36	3.114%	$175.665	$175.67	$175.65	$175.70
Purchase #6	$105.46	7.741%	$113.6237	$113.62	$113.60	$113.60
Purchase #7	$27.73	6.248%	$29.4626	$29.46	$29.45	$29.50
7 purchase totals =	$746.83		$803.5901	$803.59	$803.55	$803.60