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	$29.33	5.795%	$31.0297	$31.03	$31.05	$31.00
Purchase #2	$67.71	11.172%	$75.2746	$75.27	$75.25	$75.30
Purchase #3	$241.28	4.142%	$251.2738	$251.27	$251.25	$251.30
Purchase #4	$166.91	4.467%	$174.3659	$174.37	$174.35	$174.40
Purchase #5	$81.45	11.544%	$90.8526	$90.85	$90.85	$90.90
Purchase #6	$209.46	12.157%	$234.9241	$234.92	$234.90	$234.90
Purchase #7	$59.27	5.280%	$62.3995	$62.40	$62.40	$62.40
7 purchase totals =	$855.41		$920.1202	$920.11	$920.05	$920.20