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	$70.85	13.266%	$80.249	$80.25	$80.25	$80.20
Purchase #2	$60.28	7.826%	$64.9975	$65.00	$65.00	$65.00
Purchase #3	$51.43	3.766%	$53.3669	$53.37	$53.35	$53.40
Purchase #4	$155.56	12.594%	$175.1512	$175.15	$175.15	$175.20
Purchase #5	$221.71	9.841%	$243.5285	$243.53	$243.55	$243.50
Purchase #6	$137.37	6.611%	$146.4515	$146.45	$146.45	$146.50
Purchase #7	$160.73	13.317%	$182.1344	$182.13	$182.15	$182.10
7 purchase totals =	$857.93		$945.8790	$945.88	$945.90	$945.90