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	$199.42	6.238%	$211.8598	$211.86	$211.85	$211.90
Purchase #2	$150.49	3.635%	$155.9603	$155.96	$155.95	$156.00
Purchase #3	$119.66	3.798%	$124.2047	$124.20	$124.20	$124.20
Purchase #4	$83.89	6.609%	$89.4343	$89.43	$89.45	$89.40
Purchase #5	$142.82	5.352%	$150.4637	$150.46	$150.45	$150.50
Purchase #6	$49.84	8.692%	$54.1721	$54.17	$54.15	$54.20
Purchase #7	$118.75	4.570%	$124.1769	$124.18	$124.20	$124.20
7 purchase totals =	$864.87		$910.2718	$910.26	$910.25	$910.40