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	$43.74	12.645%	$49.2709	$49.27	$49.25	$49.30
Purchase #2	$41.53	5.266%	$43.717	$43.72	$43.70	$43.70
Purchase #3	$37.54	6.224%	$39.8765	$39.88	$39.90	$39.90
Purchase #4	$84.57	3.243%	$87.3126	$87.31	$87.30	$87.30
Purchase #5	$173.64	9.619%	$190.3424	$190.34	$190.35	$190.30
Purchase #6	$88.52	13.362%	$100.348	$100.35	$100.35	$100.30
Purchase #7	$36.42	10.518%	$40.2507	$40.25	$40.25	$40.30
7 purchase totals =	$505.96		$551.1181	$551.12	$551.10	$551.10