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	$76.93	6.617%	$82.0205	$82.02	$82.00	$82.00
Purchase #2	$190.47	6.854%	$203.5248	$203.52	$203.50	$203.50
Purchase #3	$136.46	11.642%	$152.3467	$152.35	$152.35	$152.30
Purchase #4	$79.49	10.154%	$87.5614	$87.56	$87.55	$87.60
Purchase #5	$111.27	10.865%	$123.3595	$123.36	$123.35	$123.40
Purchase #6	$60.89	13.338%	$69.0115	$69.01	$69.00	$69.00
Purchase #7	$89.94	12.850%	$101.4973	$101.50	$101.50	$101.50
7 purchase totals =	$745.45		$819.3217	$819.32	$819.25	$819.30