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	$68.45	6.451%	$72.8657	$72.87	$72.85	$72.90
Purchase #2	$97.81	11.763%	$109.3154	$109.32	$109.30	$109.30
Purchase #3	$133.72	12.507%	$150.4444	$150.44	$150.45	$150.40
Purchase #4	$106.70	10.385%	$117.7808	$117.78	$117.80	$117.80
Purchase #5	$245.60	4.729%	$257.2144	$257.21	$257.20	$257.20
Purchase #6	$83.46	3.363%	$86.2668	$86.27	$86.25	$86.30
Purchase #7	$150.72	3.402%	$155.8475	$155.85	$155.85	$155.80
7 purchase totals =	$886.46		$949.7350	$949.74	$949.70	$949.70