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	$137.94	10.619%	$152.5878	$152.59	$152.60	$152.60
Purchase #2	$79.82	3.403%	$82.5363	$82.54	$82.55	$82.50
Purchase #3	$13.84	4.172%	$14.4174	$14.42	$14.40	$14.40
Purchase #4	$24.54	3.402%	$25.3749	$25.37	$25.35	$25.40
Purchase #5	$66.64	9.854%	$73.2067	$73.21	$73.20	$73.20
Purchase #6	$149.48	10.464%	$165.1216	$165.12	$165.10	$165.10
Purchase #7	$85.58	8.190%	$92.589	$92.59	$92.60	$92.60
7 purchase totals =	$557.84		$605.8337	$605.84	$605.80	$605.80