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	$203.67	10.584%	$225.2264	$225.23	$225.25	$225.20
Purchase #2	$126.62	12.867%	$142.9122	$142.91	$142.90	$142.90
Purchase #3	$85.46	5.366%	$90.0458	$90.05	$90.05	$90.00
Purchase #4	$34.99	3.810%	$36.3231	$36.32	$36.30	$36.30
Purchase #5	$17.75	11.764%	$19.8381	$19.84	$19.85	$19.80
Purchase #6	$89.82	7.792%	$96.8188	$96.82	$96.80	$96.80
Purchase #7	$205.54	10.863%	$227.8678	$227.87	$227.85	$227.90
7 purchase totals =	$763.85		$839.0322	$839.04	$839.00	$838.90