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	$27.82	5.690%	$29.403	$29.40	$29.40	$29.40
Purchase #2	$129.34	3.836%	$134.3015	$134.30	$134.30	$134.30
Purchase #3	$38.91	4.631%	$40.7119	$40.71	$40.70	$40.70
Purchase #4	$82.36	7.491%	$88.5296	$88.53	$88.55	$88.50
Purchase #5	$48.54	5.674%	$51.2942	$51.29	$51.30	$51.30
Purchase #6	$84.91	5.264%	$89.3797	$89.38	$89.40	$89.40
Purchase #7	$180.33	4.360%	$188.1924	$188.19	$188.20	$188.20
7 purchase totals =	$592.21		$621.8123	$621.80	$621.85	$621.80