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	$40.74	7.691%	$43.8733	$43.87	$43.85	$43.90
Purchase #2	$75.43	13.254%	$85.4275	$85.43	$85.45	$85.40
Purchase #3	$35.25	9.378%	$38.5557	$38.56	$38.55	$38.60
Purchase #4	$131.28	6.717%	$140.0981	$140.10	$140.10	$140.10
Purchase #5	$38.57	5.730%	$40.7801	$40.78	$40.80	$40.80
Purchase #6	$80.80	3.727%	$83.8114	$83.81	$83.80	$83.80
Purchase #7	$55.89	6.742%	$59.6581	$59.66	$59.65	$59.70
7 purchase totals =	$457.96		$492.2042	$492.21	$492.20	$492.30