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	$201.57	9.836%	$221.3964	$221.40	$221.40	$221.40
Purchase #2	$88.82	12.496%	$99.9189	$99.92	$99.90	$99.90
Purchase #3	$101.67	13.619%	$115.5164	$115.52	$115.50	$115.50
Purchase #4	$98.78	4.608%	$103.3318	$103.33	$103.35	$103.30
Purchase #5	$98.36	5.703%	$103.9695	$103.97	$103.95	$104.00
Purchase #6	$35.53	9.336%	$38.8471	$38.85	$38.85	$38.80
Purchase #7	$134.32	6.189%	$142.6331	$142.63	$142.65	$142.60
7 purchase totals =	$759.05		$825.6132	$825.62	$825.60	$825.50