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	$81.33	11.672%	$90.8228	$90.82	$90.80	$90.80
Purchase #2	$167.33	11.318%	$186.2684	$186.27	$186.25	$186.30
Purchase #3	$58.69	9.122%	$64.0437	$64.04	$64.05	$64.00
Purchase #4	$181.49	10.416%	$200.394	$200.39	$200.40	$200.40
Purchase #5	$203.93	5.478%	$215.1013	$215.10	$215.10	$215.10
Purchase #6	$53.47	10.495%	$59.0817	$59.08	$59.10	$59.10
Purchase #7	$104.53	10.401%	$115.4022	$115.40	$115.40	$115.40
7 purchase totals =	$850.77		$931.1141	$931.10	$931.10	$931.10