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	$72.98	7.141%	$78.1915	$78.19	$78.20	$78.20
Purchase #2	$88.56	12.834%	$99.9258	$99.93	$99.95	$99.90
Purchase #3	$195.25	8.685%	$212.2075	$212.21	$212.20	$212.20
Purchase #4	$73.39	12.307%	$82.4221	$82.42	$82.40	$82.40
Purchase #5	$208.31	6.635%	$222.1314	$222.13	$222.15	$222.10
Purchase #6	$85.50	5.804%	$90.4624	$90.46	$90.45	$90.50
Purchase #7	$92.83	10.493%	$102.5707	$102.57	$102.55	$102.60
7 purchase totals =	$816.82		$887.9114	$887.91	$887.90	$887.90