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	$245.94	11.193%	$273.4681	$273.47	$273.45	$273.50
Purchase #2	$214.95	6.142%	$228.1522	$228.15	$228.15	$228.20
Purchase #3	$104.51	8.874%	$113.7842	$113.78	$113.80	$113.80
Purchase #4	$96.66	7.199%	$103.6186	$103.62	$103.60	$103.60
Purchase #5	$105.79	10.164%	$116.5425	$116.54	$116.55	$116.50
Purchase #6	$171.60	6.303%	$182.4159	$182.42	$182.40	$182.40
Purchase #7	$6.82	9.146%	$7.4438	$7.44	$7.45	$7.40
7 purchase totals =	$946.27		$1,025.4253	$1,025.42	$1,025.40	$1,025.40