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	$202.92	3.305%	$209.6265	$209.63	$209.65	$209.60
Purchase #2	$68.77	5.413%	$72.4925	$72.49	$72.50	$72.50
Purchase #3	$99.46	9.806%	$109.213	$109.21	$109.20	$109.20
Purchase #4	$194.82	11.835%	$217.8769	$217.88	$217.90	$217.90
Purchase #5	$37.61	3.801%	$39.0396	$39.04	$39.05	$39.00
Purchase #6	$5.28	6.710%	$5.6343	$5.63	$5.65	$5.60
Purchase #7	$240.30	6.329%	$255.5086	$255.51	$255.50	$255.50
7 purchase totals =	$849.16		$909.3914	$909.39	$909.45	$909.30