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	$223.38	3.544%	$231.2966	$231.30	$231.30	$231.30
Purchase #2	$214.32	6.373%	$227.9786	$227.98	$228.00	$228.00
Purchase #3	$56.66	5.595%	$59.8301	$59.83	$59.85	$59.80
Purchase #4	$11.93	7.737%	$12.853	$12.85	$12.85	$12.90
Purchase #5	$78.54	4.851%	$82.35	$82.35	$82.35	$82.40
Purchase #6	$86.33	7.841%	$93.0991	$93.10	$93.10	$93.10
Purchase #7	$128.66	3.766%	$133.5053	$133.51	$133.50	$133.50
7 purchase totals =	$799.82		$840.9127	$840.92	$840.95	$841.00