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	$99.52	11.730%	$111.1937	$111.19	$111.20	$111.20
Purchase #2	$238.46	6.538%	$254.0505	$254.05	$254.05	$254.10
Purchase #3	$59.41	5.249%	$62.5284	$62.53	$62.55	$62.50
Purchase #4	$159.94	4.494%	$167.1277	$167.13	$167.15	$167.10
Purchase #5	$171.95	12.557%	$193.5418	$193.54	$193.55	$193.50
Purchase #6	$77.63	6.740%	$82.8623	$82.86	$82.85	$82.90
Purchase #7	$106.63	9.764%	$117.0414	$117.04	$117.05	$117.00
7 purchase totals =	$913.54		$988.3458	$988.34	$988.40	$988.30