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	$115.50	5.196%	$121.5014	$121.50	$121.50	$121.50
Purchase #2	$190.96	5.659%	$201.7664	$201.77	$201.75	$201.80
Purchase #3	$29.28	12.477%	$32.9333	$32.93	$32.95	$32.90
Purchase #4	$83.83	3.539%	$86.7967	$86.80	$86.80	$86.80
Purchase #5	$131.54	13.191%	$148.8914	$148.89	$148.90	$148.90
Purchase #6	$78.25	5.721%	$82.7267	$82.73	$82.75	$82.70
Purchase #7	$77.85	7.710%	$83.8522	$83.85	$83.85	$83.90
7 purchase totals =	$707.21		$758.4681	$758.47	$758.50	$758.50