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	$29.46	13.110%	$33.3222	$33.32	$33.30	$33.30
Purchase #2	$55.55	4.250%	$57.9109	$57.91	$57.90	$57.90
Purchase #3	$55.29	13.618%	$62.8194	$62.82	$62.80	$62.80
Purchase #4	$229.79	13.838%	$261.5883	$261.59	$261.60	$261.60
Purchase #5	$202.42	4.515%	$211.5593	$211.56	$211.55	$211.60
Purchase #6	$230.59	8.680%	$250.6052	$250.61	$250.60	$250.60
Purchase #7	$185.56	3.441%	$191.9451	$191.95	$191.95	$191.90
7 purchase totals =	$988.66		$1,069.7504	$1,069.76	$1,069.70	$1,069.70