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	$103.64	5.241%	$109.0718	$109.07	$109.05	$109.10
Purchase #2	$97.83	12.598%	$110.1546	$110.15	$110.15	$110.20
Purchase #3	$34.83	8.618%	$37.8316	$37.83	$37.85	$37.80
Purchase #4	$170.94	11.215%	$190.1109	$190.11	$190.10	$190.10
Purchase #5	$100.45	8.237%	$108.7241	$108.72	$108.70	$108.70
Purchase #6	$10.34	7.301%	$11.0949	$11.09	$11.10	$11.10
Purchase #7	$185.94	12.805%	$209.7496	$209.75	$209.75	$209.70
7 purchase totals =	$703.97		$776.7375	$776.72	$776.70	$776.70