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	$74.37	5.340%	$78.3414	$78.34	$78.35	$78.30
Purchase #2	$115.97	6.551%	$123.5672	$123.57	$123.55	$123.60
Purchase #3	$238.52	9.525%	$261.239	$261.24	$261.25	$261.20
Purchase #4	$31.87	3.228%	$32.8988	$32.90	$32.90	$32.90
Purchase #5	$77.74	11.651%	$86.7975	$86.80	$86.80	$86.80
Purchase #6	$155.72	7.873%	$167.9798	$167.98	$168.00	$168.00
Purchase #7	$80.62	10.855%	$89.3713	$89.37	$89.35	$89.40
7 purchase totals =	$774.81		$840.1950	$840.20	$840.20	$840.20