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	$79.36	12.589%	$89.3506	$89.35	$89.35	$89.40
Purchase #2	$150.96	11.196%	$167.8615	$167.86	$167.85	$167.90
Purchase #3	$148.30	6.311%	$157.6592	$157.66	$157.65	$157.70
Purchase #4	$116.29	9.825%	$127.7155	$127.72	$127.70	$127.70
Purchase #5	$202.58	7.642%	$218.0612	$218.06	$218.05	$218.10
Purchase #6	$18.92	6.351%	$20.1216	$20.12	$20.10	$20.10
Purchase #7	$39.36	10.208%	$43.3779	$43.38	$43.40	$43.40
7 purchase totals =	$755.77		$824.1475	$824.15	$824.10	$824.30