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	$99.81	9.282%	$109.0744	$109.07	$109.05	$109.10
Purchase #2	$164.91	5.488%	$173.9603	$173.96	$173.95	$174.00
Purchase #3	$117.78	13.102%	$133.2115	$133.21	$133.20	$133.20
Purchase #4	$167.44	12.351%	$188.1205	$188.12	$188.10	$188.10
Purchase #5	$37.54	3.863%	$38.9902	$38.99	$39.00	$39.00
Purchase #6	$162.46	13.524%	$184.4311	$184.43	$184.45	$184.40
Purchase #7	$89.65	12.155%	$100.547	$100.55	$100.55	$100.50
7 purchase totals =	$839.59		$928.3350	$928.33	$928.30	$928.30