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	$64.56	4.592%	$67.5246	$67.52	$67.50	$67.50
Purchase #2	$134.79	6.496%	$143.546	$143.55	$143.55	$143.50
Purchase #3	$206.33	9.346%	$225.6136	$225.61	$225.60	$225.60
Purchase #4	$113.35	11.294%	$126.1517	$126.15	$126.15	$126.20
Purchase #5	$37.33	5.760%	$39.4802	$39.48	$39.50	$39.50
Purchase #6	$148.25	7.729%	$159.7082	$159.71	$159.70	$159.70
Purchase #7	$198.98	9.670%	$218.2214	$218.22	$218.20	$218.20
7 purchase totals =	$903.59		$980.2457	$980.24	$980.20	$980.20