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	$140.53	13.110%	$158.9535	$158.95	$158.95	$159.00
Purchase #2	$162.98	3.608%	$168.8603	$168.86	$168.85	$168.90
Purchase #3	$77.91	5.320%	$82.0548	$82.05	$82.05	$82.10
Purchase #4	$248.29	10.125%	$273.4294	$273.43	$273.45	$273.40
Purchase #5	$199.32	12.150%	$223.5374	$223.54	$223.55	$223.50
Purchase #6	$182.46	4.870%	$191.3458	$191.35	$191.35	$191.30
Purchase #7	$195.52	12.473%	$219.9072	$219.91	$219.90	$219.90
7 purchase totals =	$1,207.01		$1,318.0884	$1,318.09	$1,318.10	$1,318.10