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	$77.95	6.645%	$83.1298	$83.13	$83.15	$83.10
Purchase #2	$152.56	10.347%	$168.3454	$168.35	$168.35	$168.30
Purchase #3	$112.43	3.149%	$115.9704	$115.97	$115.95	$116.00
Purchase #4	$35.75	12.788%	$40.3217	$40.32	$40.30	$40.30
Purchase #5	$125.71	11.800%	$140.5438	$140.54	$140.55	$140.50
Purchase #6	$152.69	10.384%	$168.5453	$168.55	$168.55	$168.50
Purchase #7	$89.32	12.250%	$100.2617	$100.26	$100.25	$100.30
7 purchase totals =	$746.41		$817.1181	$817.12	$817.10	$817.00