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	$45.82	9.434%	$50.1427	$50.14	$50.15	$50.10
Purchase #2	$206.97	12.735%	$233.3276	$233.33	$233.35	$233.30
Purchase #3	$63.73	5.629%	$67.3174	$67.32	$67.30	$67.30
Purchase #4	$172.81	8.555%	$187.5939	$187.59	$187.60	$187.60
Purchase #5	$208.91	7.134%	$223.8136	$223.81	$223.80	$223.80
Purchase #6	$117.89	5.333%	$124.1771	$124.18	$124.20	$124.20
Purchase #7	$103.47	7.135%	$110.8526	$110.85	$110.85	$110.90
7 purchase totals =	$919.60		$997.2249	$997.22	$997.25	$997.20