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	$169.90	13.643%	$193.0795	$193.08	$193.10	$193.10
Purchase #2	$215.50	12.265%	$241.9311	$241.93	$241.95	$241.90
Purchase #3	$102.34	10.471%	$113.056	$113.06	$113.05	$113.10
Purchase #4	$48.69	3.261%	$50.2778	$50.28	$50.30	$50.30
Purchase #5	$78.34	13.740%	$89.1039	$89.10	$89.10	$89.10
Purchase #6	$25.86	7.359%	$27.763	$27.76	$27.75	$27.80
Purchase #7	$155.71	5.586%	$164.408	$164.41	$164.40	$164.40
7 purchase totals =	$796.34		$879.6193	$879.62	$879.65	$879.70