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	$71.70	12.359%	$80.5614	$80.56	$80.55	$80.60
Purchase #2	$25.67	9.254%	$28.0455	$28.05	$28.05	$28.00
Purchase #3	$105.29	10.745%	$116.6034	$116.60	$116.60	$116.60
Purchase #4	$13.72	6.287%	$14.5826	$14.58	$14.60	$14.60
Purchase #5	$142.74	5.629%	$150.7748	$150.77	$150.75	$150.80
Purchase #6	$237.62	11.648%	$265.298	$265.30	$265.30	$265.30
Purchase #7	$120.71	6.357%	$128.3835	$128.38	$128.40	$128.40
7 purchase totals =	$717.45		$784.2492	$784.24	$784.25	$784.30