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	$47.94	6.846%	$51.222	$51.22	$51.20	$51.20
Purchase #2	$211.90	13.412%	$240.32	$240.32	$240.30	$240.30
Purchase #3	$130.46	6.138%	$138.4676	$138.47	$138.45	$138.50
Purchase #4	$29.95	9.460%	$32.7833	$32.78	$32.80	$32.80
Purchase #5	$215.29	4.262%	$224.4657	$224.47	$224.45	$224.50
Purchase #6	$197.41	13.288%	$223.6418	$223.64	$223.65	$223.60
Purchase #7	$95.33	5.802%	$100.861	$100.86	$100.85	$100.90
7 purchase totals =	$928.28		$1,011.7614	$1,011.76	$1,011.70	$1,011.80