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	$19.54	4.341%	$20.3882	$20.39	$20.40	$20.40
Purchase #2	$117.63	5.611%	$124.2302	$124.23	$124.25	$124.20
Purchase #3	$57.77	3.554%	$59.8231	$59.82	$59.80	$59.80
Purchase #4	$111.68	4.170%	$116.3371	$116.34	$116.35	$116.30
Purchase #5	$203.63	10.266%	$224.5347	$224.53	$224.55	$224.50
Purchase #6	$95.32	11.703%	$106.4753	$106.48	$106.50	$106.50
Purchase #7	$187.47	5.749%	$198.2477	$198.25	$198.25	$198.20
7 purchase totals =	$793.04		$850.0363	$850.04	$850.10	$849.90