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	$51.56	10.713%	$57.0836	$57.08	$57.10	$57.10
Purchase #2	$235.71	13.400%	$267.2951	$267.30	$267.30	$267.30
Purchase #3	$199.56	12.163%	$223.8325	$223.83	$223.85	$223.80
Purchase #4	$159.33	13.595%	$180.9909	$180.99	$181.00	$181.00
Purchase #5	$136.83	10.338%	$150.9755	$150.98	$151.00	$151.00
Purchase #6	$158.82	3.834%	$164.9092	$164.91	$164.90	$164.90
Purchase #7	$106.51	6.225%	$113.1402	$113.14	$113.15	$113.10
7 purchase totals =	$1,048.32		$1,158.2270	$1,158.23	$1,158.30	$1,158.20