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	$79.85	12.748%	$90.0293	$90.03	$90.05	$90.00
Purchase #2	$52.36	6.658%	$55.8461	$55.85	$55.85	$55.80
Purchase #3	$199.53	4.268%	$208.0459	$208.05	$208.05	$208.00
Purchase #4	$167.77	13.533%	$190.4743	$190.47	$190.45	$190.50
Purchase #5	$226.32	7.568%	$243.4479	$243.45	$243.45	$243.40
Purchase #6	$180.53	4.138%	$188.0003	$188.00	$188.00	$188.00
Purchase #7	$34.96	3.245%	$36.0945	$36.09	$36.10	$36.10
7 purchase totals =	$941.32		$1,011.9383	$1,011.94	$1,011.95	$1,011.80