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	$77.64	3.120%	$80.0624	$80.06	$80.05	$80.10
Purchase #2	$184.85	6.361%	$196.6083	$196.61	$196.60	$196.60
Purchase #3	$105.97	10.571%	$117.1721	$117.17	$117.15	$117.20
Purchase #4	$61.59	13.328%	$69.7987	$69.80	$69.80	$69.80
Purchase #5	$152.45	6.373%	$162.1656	$162.17	$162.15	$162.20
Purchase #6	$93.38	13.763%	$106.2319	$106.23	$106.25	$106.20
Purchase #7	$182.60	7.259%	$195.8549	$195.85	$195.85	$195.90
7 purchase totals =	$858.48		$927.8939	$927.89	$927.85	$928.00