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	$81.33	4.860%	$85.2826	$85.28	$85.30	$85.30
Purchase #2	$62.94	6.745%	$67.1853	$67.19	$67.20	$67.20
Purchase #3	$108.37	7.254%	$116.2312	$116.23	$116.25	$116.20
Purchase #4	$92.40	9.869%	$101.519	$101.52	$101.50	$101.50
Purchase #5	$241.27	11.677%	$269.4431	$269.44	$269.45	$269.40
Purchase #6	$235.76	11.369%	$262.5636	$262.56	$262.55	$262.60
Purchase #7	$90.41	7.430%	$97.1275	$97.13	$97.15	$97.10
7 purchase totals =	$912.48		$999.3523	$999.35	$999.40	$999.30