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	$52.47	8.358%	$56.8554	$56.86	$56.85	$56.90
Purchase #2	$124.66	5.252%	$131.2071	$131.21	$131.20	$131.20
Purchase #3	$105.49	4.830%	$110.5852	$110.59	$110.60	$110.60
Purchase #4	$73.44	4.316%	$76.6097	$76.61	$76.60	$76.60
Purchase #5	$94.71	7.238%	$101.5651	$101.57	$101.55	$101.60
Purchase #6	$52.66	12.862%	$59.4331	$59.43	$59.45	$59.40
Purchase #7	$76.81	3.586%	$79.5644	$79.56	$79.55	$79.60
7 purchase totals =	$580.24		$615.8200	$615.83	$615.80	$615.90