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	$91.86	9.292%	$100.3956	$100.40	$100.40	$100.40
Purchase #2	$96.44	13.278%	$109.2453	$109.25	$109.25	$109.20
Purchase #3	$79.80	12.364%	$89.6665	$89.67	$89.65	$89.70
Purchase #4	$71.78	10.383%	$79.2329	$79.23	$79.25	$79.20
Purchase #5	$88.55	7.267%	$94.9849	$94.98	$95.00	$95.00
Purchase #6	$40.94	7.196%	$43.886	$43.89	$43.90	$43.90
Purchase #7	$19.54	10.853%	$21.6607	$21.66	$21.65	$21.70
7 purchase totals =	$488.91		$539.0719	$539.08	$539.10	$539.10