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	$78.73	13.354%	$89.2436	$89.24	$89.25	$89.20
Purchase #2	$64.76	11.396%	$72.14	$72.14	$72.15	$72.10
Purchase #3	$166.28	8.841%	$180.9808	$180.98	$181.00	$181.00
Purchase #4	$213.76	13.139%	$241.8459	$241.85	$241.85	$241.80
Purchase #5	$69.83	6.713%	$74.5177	$74.52	$74.50	$74.50
Purchase #6	$6.71	9.304%	$7.3343	$7.33	$7.35	$7.30
Purchase #7	$108.96	6.731%	$116.2941	$116.29	$116.30	$116.30
7 purchase totals =	$709.03		$782.3564	$782.35	$782.40	$782.20