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	$64.32	8.257%	$69.6309	$69.63	$69.65	$69.60
Purchase #2	$137.78	13.825%	$156.8281	$156.83	$156.85	$156.80
Purchase #3	$58.75	10.329%	$64.8183	$64.82	$64.80	$64.80
Purchase #4	$238.54	13.520%	$270.7906	$270.79	$270.80	$270.80
Purchase #5	$115.73	3.700%	$120.012	$120.01	$120.00	$120.00
Purchase #6	$139.83	3.589%	$144.8485	$144.85	$144.85	$144.80
Purchase #7	$29.94	11.470%	$33.3741	$33.37	$33.35	$33.40
7 purchase totals =	$784.89		$860.3025	$860.30	$860.30	$860.20