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	$100.62	4.270%	$104.9165	$104.92	$104.90	$104.90
Purchase #2	$38.63	9.551%	$42.3196	$42.32	$42.30	$42.30
Purchase #3	$155.91	3.284%	$161.0301	$161.03	$161.05	$161.00
Purchase #4	$25.41	6.630%	$27.0947	$27.09	$27.10	$27.10
Purchase #5	$60.35	3.228%	$62.2981	$62.30	$62.30	$62.30
Purchase #6	$151.89	8.337%	$164.5531	$164.55	$164.55	$164.60
Purchase #7	$89.53	11.611%	$99.9253	$99.93	$99.95	$99.90
7 purchase totals =	$622.34		$662.1374	$662.14	$662.15	$662.10