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	$188.67	5.231%	$198.5393	$198.54	$198.55	$198.50
Purchase #2	$36.91	12.348%	$41.4676	$41.47	$41.45	$41.50
Purchase #3	$49.44	10.475%	$54.6188	$54.62	$54.60	$54.60
Purchase #4	$8.55	7.839%	$9.2202	$9.22	$9.20	$9.20
Purchase #5	$11.92	3.786%	$12.3713	$12.37	$12.35	$12.40
Purchase #6	$93.90	6.144%	$99.6692	$99.67	$99.65	$99.70
Purchase #7	$81.36	10.706%	$90.0704	$90.07	$90.05	$90.10
7 purchase totals =	$470.75		$505.9568	$505.96	$505.85	$506.00