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	$69.75	12.139%	$78.217	$78.22	$78.20	$78.20
Purchase #2	$84.38	10.115%	$92.915	$92.92	$92.90	$92.90
Purchase #3	$219.98	13.672%	$250.0557	$250.06	$250.05	$250.10
Purchase #4	$59.51	12.821%	$67.1398	$67.14	$67.15	$67.10
Purchase #5	$123.68	4.819%	$129.6401	$129.64	$129.65	$129.60
Purchase #6	$226.62	10.182%	$249.6944	$249.69	$249.70	$249.70
Purchase #7	$228.75	9.434%	$250.3303	$250.33	$250.35	$250.30
7 purchase totals =	$1,012.67		$1,117.9923	$1,118.00	$1,118.00	$1,117.90