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	$48.91	13.360%	$55.4444	$55.44	$55.45	$55.40
Purchase #2	$235.58	11.657%	$263.0416	$263.04	$263.05	$263.00
Purchase #3	$37.78	7.164%	$40.4866	$40.49	$40.50	$40.50
Purchase #4	$105.74	11.460%	$117.8578	$117.86	$117.85	$117.90
Purchase #5	$240.34	8.841%	$261.5885	$261.59	$261.60	$261.60
Purchase #6	$165.87	10.666%	$183.5617	$183.56	$183.55	$183.60
Purchase #7	$167.69	13.272%	$189.9458	$189.95	$189.95	$189.90
7 purchase totals =	$1,001.91		$1,111.9264	$1,111.93	$1,111.95	$1,111.90