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	$38.60	7.505%	$41.4969	$41.50	$41.50	$41.50
Purchase #2	$91.46	8.758%	$99.4701	$99.47	$99.45	$99.50
Purchase #3	$140.74	11.216%	$156.5254	$156.53	$156.55	$156.50
Purchase #4	$120.83	8.265%	$130.8166	$130.82	$130.80	$130.80
Purchase #5	$161.79	9.339%	$176.8996	$176.90	$176.90	$176.90
Purchase #6	$92.53	13.456%	$104.9808	$104.98	$105.00	$105.00
Purchase #7	$72.40	11.436%	$80.6797	$80.68	$80.70	$80.70
7 purchase totals =	$718.35		$790.8691	$790.88	$790.90	$790.90