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	$250.80	10.233%	$276.4644	$276.46	$276.45	$276.50
Purchase #2	$203.63	10.575%	$225.1639	$225.16	$225.15	$225.20
Purchase #3	$39.69	8.110%	$42.9089	$42.91	$42.90	$42.90
Purchase #4	$73.50	4.424%	$76.7516	$76.75	$76.75	$76.80
Purchase #5	$238.96	3.312%	$246.8744	$246.87	$246.85	$246.90
Purchase #6	$119.76	6.777%	$127.8761	$127.88	$127.90	$127.90
Purchase #7	$61.85	10.766%	$68.5088	$68.51	$68.50	$68.50
7 purchase totals =	$988.19		$1,064.5481	$1,064.54	$1,064.50	$1,064.70