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	$30.35	10.666%	$33.5871	$33.59	$33.60	$33.60
Purchase #2	$250.61	9.750%	$275.0445	$275.04	$275.05	$275.00
Purchase #3	$181.69	5.473%	$191.6339	$191.63	$191.65	$191.60
Purchase #4	$28.75	11.237%	$31.9806	$31.98	$32.00	$32.00
Purchase #5	$29.72	5.350%	$31.31	$31.31	$31.30	$31.30
Purchase #6	$39.84	4.649%	$41.6922	$41.69	$41.70	$41.70
Purchase #7	$155.93	3.567%	$161.492	$161.49	$161.50	$161.50
7 purchase totals =	$716.89		$766.7403	$766.73	$766.80	$766.70