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	$25.60	12.213%	$28.7265	$28.73	$28.75	$28.70
Purchase #2	$91.85	3.538%	$95.0997	$95.10	$95.10	$95.10
Purchase #3	$80.93	11.615%	$90.33	$90.33	$90.35	$90.30
Purchase #4	$68.55	5.398%	$72.2503	$72.25	$72.25	$72.30
Purchase #5	$24.75	13.530%	$28.0987	$28.10	$28.10	$28.10
Purchase #6	$68.39	3.274%	$70.6291	$70.63	$70.65	$70.60
Purchase #7	$174.62	8.786%	$189.9621	$189.96	$189.95	$190.00
7 purchase totals =	$534.69		$575.0964	$575.10	$575.15	$575.10