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	$89.33	12.272%	$100.2926	$100.29	$100.30	$100.30
Purchase #2	$81.63	9.326%	$89.2428	$89.24	$89.25	$89.20
Purchase #3	$145.36	12.109%	$162.9616	$162.96	$162.95	$163.00
Purchase #4	$147.32	4.484%	$153.9258	$153.93	$153.95	$153.90
Purchase #5	$167.38	8.641%	$181.8433	$181.84	$181.85	$181.80
Purchase #6	$139.81	10.123%	$153.963	$153.96	$153.95	$154.00
Purchase #7	$157.33	6.208%	$167.097	$167.10	$167.10	$167.10
7 purchase totals =	$928.16		$1,009.3261	$1,009.32	$1,009.35	$1,009.30