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	$92.37	6.648%	$98.5108	$98.51	$98.50	$98.50
Purchase #2	$106.74	9.497%	$116.8771	$116.88	$116.90	$116.90
Purchase #3	$78.83	9.826%	$86.5758	$86.58	$86.60	$86.60
Purchase #4	$5.59	13.150%	$6.3251	$6.33	$6.35	$6.30
Purchase #5	$72.97	13.517%	$82.8334	$82.83	$82.85	$82.80
Purchase #6	$26.53	7.545%	$28.5317	$28.53	$28.55	$28.50
Purchase #7	$146.75	12.155%	$164.5875	$164.59	$164.60	$164.60
7 purchase totals =	$529.78		$584.2414	$584.25	$584.35	$584.20