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	$234.50	4.144%	$244.2177	$244.22	$244.20	$244.20
Purchase #2	$58.33	7.796%	$62.8774	$62.88	$62.90	$62.90
Purchase #3	$11.89	8.559%	$12.9077	$12.91	$12.90	$12.90
Purchase #4	$161.83	5.872%	$171.3327	$171.33	$171.35	$171.30
Purchase #5	$98.67	13.673%	$112.1611	$112.16	$112.15	$112.20
Purchase #6	$168.74	12.653%	$190.0907	$190.09	$190.10	$190.10
Purchase #7	$81.94	7.329%	$87.9454	$87.95	$87.95	$87.90
7 purchase totals =	$815.90		$881.5327	$881.54	$881.55	$881.50