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	$74.55	10.618%	$82.4657	$82.47	$82.45	$82.50
Purchase #2	$135.43	8.163%	$146.4852	$146.49	$146.50	$146.50
Purchase #3	$44.54	3.524%	$46.1096	$46.11	$46.10	$46.10
Purchase #4	$67.77	6.706%	$72.3147	$72.31	$72.30	$72.30
Purchase #5	$114.81	8.540%	$124.6148	$124.61	$124.60	$124.60
Purchase #6	$138.93	9.651%	$152.3381	$152.34	$152.35	$152.30
Purchase #7	$156.70	11.184%	$174.2253	$174.23	$174.25	$174.20
7 purchase totals =	$732.73		$798.5534	$798.56	$798.55	$798.50