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	$115.94	6.618%	$123.6129	$123.61	$123.60	$123.60
Purchase #2	$176.74	5.818%	$187.0227	$187.02	$187.00	$187.00
Purchase #3	$243.44	13.300%	$275.8175	$275.82	$275.80	$275.80
Purchase #4	$83.61	11.823%	$93.4952	$93.50	$93.50	$93.50
Purchase #5	$123.84	11.311%	$137.8475	$137.85	$137.85	$137.80
Purchase #6	$126.65	8.447%	$137.3481	$137.35	$137.35	$137.30
Purchase #7	$22.73	4.499%	$23.7526	$23.75	$23.75	$23.80
7 purchase totals =	$892.95		$978.8965	$978.90	$978.85	$978.80