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	$77.73	13.530%	$88.2469	$88.25	$88.25	$88.20
Purchase #2	$229.83	10.677%	$254.3689	$254.37	$254.35	$254.40
Purchase #3	$76.25	12.553%	$85.8217	$85.82	$85.80	$85.80
Purchase #4	$157.30	13.292%	$178.2083	$178.21	$178.20	$178.20
Purchase #5	$145.82	6.256%	$154.9425	$154.94	$154.95	$154.90
Purchase #6	$160.48	5.130%	$168.7126	$168.71	$168.70	$168.70
Purchase #7	$36.90	9.318%	$40.3383	$40.34	$40.35	$40.30
7 purchase totals =	$884.31		$970.6392	$970.64	$970.60	$970.50