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	$99.43	13.774%	$113.1255	$113.13	$113.15	$113.10
Purchase #2	$103.99	4.799%	$108.9805	$108.98	$109.00	$109.00
Purchase #3	$135.35	7.294%	$145.2224	$145.22	$145.20	$145.20
Purchase #4	$54.85	12.121%	$61.4984	$61.50	$61.50	$61.50
Purchase #5	$55.38	6.800%	$59.1458	$59.15	$59.15	$59.10
Purchase #6	$71.31	4.641%	$74.6195	$74.62	$74.60	$74.60
Purchase #7	$25.36	12.520%	$28.5351	$28.54	$28.55	$28.50
7 purchase totals =	$545.67		$591.1272	$591.14	$591.15	$591.00