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	$122.29	8.426%	$132.5942	$132.59	$132.60	$132.60
Purchase #2	$215.83	12.511%	$242.8325	$242.83	$242.85	$242.80
Purchase #3	$178.71	4.305%	$186.4035	$186.40	$186.40	$186.40
Purchase #4	$160.69	13.679%	$182.6708	$182.67	$182.65	$182.70
Purchase #5	$135.98	7.672%	$146.4124	$146.41	$146.40	$146.40
Purchase #6	$210.96	5.526%	$222.6176	$222.62	$222.60	$222.60
Purchase #7	$136.26	4.407%	$142.265	$142.27	$142.25	$142.30
7 purchase totals =	$1,160.72		$1,255.7960	$1,255.79	$1,255.75	$1,255.80