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	$36.25	6.631%	$38.6537	$38.65	$38.65	$38.70
Purchase #2	$109.54	13.361%	$124.1756	$124.18	$124.20	$124.20
Purchase #3	$16.69	9.491%	$18.274	$18.27	$18.25	$18.30
Purchase #4	$106.94	5.491%	$112.8121	$112.81	$112.80	$112.80
Purchase #5	$39.73	7.608%	$42.7527	$42.75	$42.75	$42.80
Purchase #6	$110.70	9.180%	$120.8623	$120.86	$120.85	$120.90
Purchase #7	$52.51	12.383%	$59.0123	$59.01	$59.00	$59.00
7 purchase totals =	$472.36		$516.5427	$516.53	$516.50	$516.70