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	$108.82	6.379%	$115.7616	$115.76	$115.75	$115.80
Purchase #2	$59.37	4.808%	$62.2245	$62.22	$62.20	$62.20
Purchase #3	$218.57	11.686%	$244.1121	$244.11	$244.10	$244.10
Purchase #4	$33.73	13.204%	$38.1837	$38.18	$38.20	$38.20
Purchase #5	$63.28	7.244%	$67.864	$67.86	$67.85	$67.90
Purchase #6	$136.91	3.319%	$141.454	$141.45	$141.45	$141.50
Purchase #7	$64.87	12.277%	$72.8341	$72.83	$72.85	$72.80
7 purchase totals =	$685.55		$742.4340	$742.41	$742.40	$742.50