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	$61.32	7.665%	$66.0202	$66.02	$66.00	$66.00
Purchase #2	$54.41	9.798%	$59.7411	$59.74	$59.75	$59.70
Purchase #3	$31.36	4.601%	$32.8029	$32.80	$32.80	$32.80
Purchase #4	$169.41	12.191%	$190.0628	$190.06	$190.05	$190.10
Purchase #5	$198.65	11.275%	$221.0478	$221.05	$221.05	$221.00
Purchase #6	$99.52	6.511%	$105.9997	$106.00	$106.00	$106.00
Purchase #7	$209.98	8.819%	$228.4981	$228.50	$228.50	$228.50
7 purchase totals =	$824.65		$904.1726	$904.17	$904.15	$904.10