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	$37.44	8.505%	$40.6243	$40.62	$40.60	$40.60
Purchase #2	$168.55	11.737%	$188.3327	$188.33	$188.35	$188.30
Purchase #3	$249.27	9.552%	$273.0803	$273.08	$273.10	$273.10
Purchase #4	$209.34	4.717%	$219.2146	$219.21	$219.20	$219.20
Purchase #5	$215.59	4.492%	$225.2743	$225.27	$225.25	$225.30
Purchase #6	$116.82	8.295%	$126.5102	$126.51	$126.50	$126.50
Purchase #7	$155.27	12.338%	$174.4272	$174.43	$174.45	$174.40
7 purchase totals =	$1,152.28		$1,247.4636	$1,247.45	$1,247.45	$1,247.40