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	$106.94	6.541%	$113.9349	$113.93	$113.95	$113.90
Purchase #2	$44.81	5.341%	$47.2033	$47.20	$47.20	$47.20
Purchase #3	$246.83	12.834%	$278.5082	$278.51	$278.50	$278.50
Purchase #4	$9.43	10.316%	$10.4028	$10.40	$10.40	$10.40
Purchase #5	$83.72	6.372%	$89.0546	$89.05	$89.05	$89.10
Purchase #6	$142.40	9.819%	$156.3823	$156.38	$156.40	$156.40
Purchase #7	$117.44	12.237%	$131.8111	$131.81	$131.80	$131.80
7 purchase totals =	$751.57		$827.2972	$827.28	$827.30	$827.30