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	$137.85	6.601%	$146.9495	$146.95	$146.95	$146.90
Purchase #2	$76.54	12.373%	$86.0103	$86.01	$86.00	$86.00
Purchase #3	$89.56	10.182%	$98.679	$98.68	$98.70	$98.70
Purchase #4	$99.66	9.465%	$109.0928	$109.09	$109.10	$109.10
Purchase #5	$101.79	11.726%	$113.7259	$113.73	$113.75	$113.70
Purchase #6	$157.28	10.515%	$173.818	$173.82	$173.80	$173.80
Purchase #7	$125.61	4.737%	$131.5601	$131.56	$131.55	$131.60
7 purchase totals =	$788.29		$859.8356	$859.84	$859.85	$859.80