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	$170.44	5.278%	$179.4358	$179.44	$179.45	$179.40
Purchase #2	$212.35	5.425%	$223.87	$223.87	$223.85	$223.90
Purchase #3	$30.38	10.142%	$33.4611	$33.46	$33.45	$33.50
Purchase #4	$27.73	13.168%	$31.3815	$31.38	$31.40	$31.40
Purchase #5	$39.89	12.253%	$44.7777	$44.78	$44.80	$44.80
Purchase #6	$116.49	9.214%	$127.2234	$127.22	$127.20	$127.20
Purchase #7	$208.25	12.672%	$234.6394	$234.64	$234.65	$234.60
7 purchase totals =	$805.53		$874.7889	$874.79	$874.80	$874.80