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	$222.25	4.452%	$232.1446	$232.14	$232.15	$232.10
Purchase #2	$38.57	10.854%	$42.7564	$42.76	$42.75	$42.80
Purchase #3	$150.60	13.402%	$170.7834	$170.78	$170.80	$170.80
Purchase #4	$73.67	11.558%	$82.1848	$82.18	$82.20	$82.20
Purchase #5	$108.75	10.549%	$120.222	$120.22	$120.20	$120.20
Purchase #6	$109.99	12.299%	$123.5177	$123.52	$123.50	$123.50
Purchase #7	$84.65	5.236%	$89.0823	$89.08	$89.10	$89.10
7 purchase totals =	$788.48		$860.6912	$860.68	$860.70	$860.70