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	$136.82	5.317%	$144.0947	$144.09	$144.10	$144.10
Purchase #2	$80.34	12.477%	$90.364	$90.36	$90.35	$90.40
Purchase #3	$30.57	4.475%	$31.938	$31.94	$31.95	$31.90
Purchase #4	$42.65	12.623%	$48.0337	$48.03	$48.05	$48.00
Purchase #5	$89.93	11.851%	$100.5876	$100.59	$100.60	$100.60
Purchase #6	$166.93	9.424%	$182.6615	$182.66	$182.65	$182.70
Purchase #7	$155.71	9.195%	$170.0275	$170.03	$170.05	$170.00
7 purchase totals =	$702.95		$767.7070	$767.70	$767.75	$767.70