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	$29.74	12.274%	$33.3903	$33.39	$33.40	$33.40
Purchase #2	$97.39	3.815%	$101.1054	$101.11	$101.10	$101.10
Purchase #3	$102.75	8.314%	$111.2926	$111.29	$111.30	$111.30
Purchase #4	$123.58	10.168%	$136.1456	$136.15	$136.15	$136.10
Purchase #5	$115.44	4.551%	$120.6937	$120.69	$120.70	$120.70
Purchase #6	$90.25	8.750%	$98.1469	$98.15	$98.15	$98.10
Purchase #7	$30.62	10.457%	$33.8219	$33.82	$33.80	$33.80
7 purchase totals =	$589.77		$634.5964	$634.60	$634.60	$634.50