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	$30.73	11.331%	$34.212	$34.21	$34.20	$34.20
Purchase #2	$37.57	6.394%	$39.9722	$39.97	$39.95	$40.00
Purchase #3	$238.91	12.401%	$268.5372	$268.54	$268.55	$268.50
Purchase #4	$134.64	7.352%	$144.5387	$144.54	$144.55	$144.50
Purchase #5	$134.78	6.848%	$144.0097	$144.01	$144.00	$144.00
Purchase #6	$145.83	5.738%	$154.1977	$154.20	$154.20	$154.20
Purchase #7	$79.81	12.108%	$89.4734	$89.47	$89.45	$89.50
7 purchase totals =	$802.27		$874.9409	$874.94	$874.90	$874.90