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	$27.86	6.640%	$29.7099	$29.71	$29.70	$29.70
Purchase #2	$42.61	4.173%	$44.3881	$44.39	$44.40	$44.40
Purchase #3	$24.57	5.405%	$25.898	$25.90	$25.90	$25.90
Purchase #4	$79.97	11.565%	$89.2185	$89.22	$89.20	$89.20
Purchase #5	$56.41	9.423%	$61.7255	$61.73	$61.75	$61.70
Purchase #6	$116.86	4.686%	$122.3361	$122.34	$122.35	$122.30
Purchase #7	$174.45	12.580%	$196.3958	$196.40	$196.40	$196.40
7 purchase totals =	$522.73		$569.6719	$569.69	$569.70	$569.60