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	$62.89	4.228%	$65.549	$65.55	$65.55	$65.50
Purchase #2	$233.81	13.659%	$265.7461	$265.75	$265.75	$265.70
Purchase #3	$27.71	12.234%	$31.1	$31.10	$31.10	$31.10
Purchase #4	$74.89	3.503%	$77.5134	$77.51	$77.50	$77.50
Purchase #5	$162.68	10.684%	$180.0607	$180.06	$180.05	$180.10
Purchase #6	$19.57	3.847%	$20.3229	$20.32	$20.30	$20.30
Purchase #7	$150.66	6.328%	$160.1938	$160.19	$160.20	$160.20
7 purchase totals =	$732.21		$800.4859	$800.48	$800.45	$800.40