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	$19.73	4.139%	$20.5466	$20.55	$20.55	$20.50
Purchase #2	$161.93	5.700%	$171.16	$171.16	$171.15	$171.20
Purchase #3	$69.46	4.296%	$72.444	$72.44	$72.45	$72.40
Purchase #4	$230.85	10.302%	$254.6322	$254.63	$254.65	$254.60
Purchase #5	$81.47	6.235%	$86.5497	$86.55	$86.55	$86.50
Purchase #6	$49.70	4.317%	$51.8455	$51.85	$51.85	$51.80
Purchase #7	$128.95	6.860%	$137.796	$137.80	$137.80	$137.80
7 purchase totals =	$742.09		$794.9740	$794.98	$795.00	$794.80