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	$186.40	7.542%	$200.4583	$200.46	$200.45	$200.50
Purchase #2	$152.57	10.398%	$168.4342	$168.43	$168.45	$168.40
Purchase #3	$135.78	3.873%	$141.0388	$141.04	$141.05	$141.00
Purchase #4	$160.80	4.632%	$168.2483	$168.25	$168.25	$168.20
Purchase #5	$95.84	5.701%	$101.3038	$101.30	$101.30	$101.30
Purchase #6	$28.85	10.128%	$31.7719	$31.77	$31.75	$31.80
Purchase #7	$45.92	6.814%	$49.049	$49.05	$49.05	$49.00
7 purchase totals =	$806.16		$860.3043	$860.30	$860.30	$860.20