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	$139.49	6.339%	$148.3323	$148.33	$148.35	$148.30
Purchase #2	$240.69	6.125%	$255.4323	$255.43	$255.45	$255.40
Purchase #3	$132.66	9.199%	$144.8634	$144.86	$144.85	$144.90
Purchase #4	$123.46	6.868%	$131.9392	$131.94	$131.95	$131.90
Purchase #5	$209.62	13.747%	$238.4365	$238.44	$238.45	$238.40
Purchase #6	$205.54	10.465%	$227.0498	$227.05	$227.05	$227.00
Purchase #7	$116.87	6.573%	$124.5519	$124.55	$124.55	$124.60
7 purchase totals =	$1,168.33		$1,270.6054	$1,270.60	$1,270.65	$1,270.50