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	$32.71	13.173%	$37.0189	$37.02	$37.00	$37.00
Purchase #2	$145.45	7.167%	$155.8744	$155.87	$155.85	$155.90
Purchase #3	$102.39	3.516%	$105.99	$105.99	$106.00	$106.00
Purchase #4	$52.26	13.729%	$59.4348	$59.43	$59.45	$59.40
Purchase #5	$125.44	12.871%	$141.5854	$141.59	$141.60	$141.60
Purchase #6	$13.91	4.699%	$14.5636	$14.56	$14.55	$14.60
Purchase #7	$142.32	9.615%	$156.0041	$156.00	$156.00	$156.00
7 purchase totals =	$614.48		$670.4712	$670.46	$670.45	$670.50