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	$146.49	6.660%	$156.2462	$156.25	$156.25	$156.20
Purchase #2	$169.74	6.553%	$180.8631	$180.86	$180.85	$180.90
Purchase #3	$130.26	10.693%	$144.1887	$144.19	$144.20	$144.20
Purchase #4	$33.30	7.118%	$35.6703	$35.67	$35.65	$35.70
Purchase #5	$124.72	13.328%	$141.3427	$141.34	$141.35	$141.30
Purchase #6	$123.87	10.566%	$136.9581	$136.96	$136.95	$137.00
Purchase #7	$120.69	6.571%	$128.6205	$128.62	$128.60	$128.60
7 purchase totals =	$849.07		$923.8896	$923.89	$923.85	$923.90