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	$63.86	9.796%	$70.1157	$70.12	$70.10	$70.10
Purchase #2	$206.86	9.291%	$226.0794	$226.08	$226.10	$226.10
Purchase #3	$33.93	11.682%	$37.8937	$37.89	$37.90	$37.90
Purchase #4	$152.59	13.686%	$173.4735	$173.47	$173.45	$173.50
Purchase #5	$115.44	10.522%	$127.5866	$127.59	$127.60	$127.60
Purchase #6	$84.35	13.669%	$95.8798	$95.88	$95.90	$95.90
Purchase #7	$167.30	13.499%	$189.8838	$189.88	$189.90	$189.90
7 purchase totals =	$824.33		$920.9125	$920.91	$920.95	$921.00