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	$133.43	7.469%	$143.3959	$143.40	$143.40	$143.40
Purchase #2	$240.51	9.844%	$264.1858	$264.19	$264.20	$264.20
Purchase #3	$230.36	8.115%	$249.0537	$249.05	$249.05	$249.10
Purchase #4	$99.90	3.605%	$103.5014	$103.50	$103.50	$103.50
Purchase #5	$54.29	4.836%	$56.9155	$56.92	$56.90	$56.90
Purchase #6	$194.65	4.321%	$203.0608	$203.06	$203.05	$203.10
Purchase #7	$84.33	6.411%	$89.7364	$89.74	$89.75	$89.70
7 purchase totals =	$1,037.47		$1,109.8495	$1,109.86	$1,109.85	$1,109.90