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	$6.39	11.419%	$7.1197	$7.12	$7.10	$7.10
Purchase #2	$36.92	7.107%	$39.5439	$39.54	$39.55	$39.50
Purchase #3	$219.44	12.363%	$246.5694	$246.57	$246.55	$246.60
Purchase #4	$52.71	13.117%	$59.624	$59.62	$59.60	$59.60
Purchase #5	$39.32	5.315%	$41.4099	$41.41	$41.40	$41.40
Purchase #6	$78.46	9.501%	$85.9145	$85.91	$85.90	$85.90
Purchase #7	$134.86	5.544%	$142.3366	$142.34	$142.35	$142.30
7 purchase totals =	$568.10		$622.5180	$622.51	$622.45	$622.40