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	$86.98	12.111%	$97.5141	$97.51	$97.50	$97.50
Purchase #2	$64.37	8.139%	$69.6091	$69.61	$69.60	$69.60
Purchase #3	$90.56	4.376%	$94.5229	$94.52	$94.50	$94.50
Purchase #4	$41.79	5.146%	$43.9405	$43.94	$43.95	$43.90
Purchase #5	$41.84	12.356%	$47.0098	$47.01	$47.00	$47.00
Purchase #6	$122.85	7.143%	$131.6252	$131.63	$131.65	$131.60
Purchase #7	$93.39	6.676%	$99.6247	$99.62	$99.60	$99.60
7 purchase totals =	$541.78		$583.8463	$583.84	$583.80	$583.70