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	$99.47	3.870%	$103.3195	$103.32	$103.30	$103.30
Purchase #2	$70.93	9.768%	$77.8584	$77.86	$77.85	$77.90
Purchase #3	$243.55	8.583%	$264.4539	$264.45	$264.45	$264.50
Purchase #4	$144.85	5.425%	$152.7081	$152.71	$152.70	$152.70
Purchase #5	$53.37	10.737%	$59.1003	$59.10	$59.10	$59.10
Purchase #6	$181.35	5.658%	$191.6108	$191.61	$191.60	$191.60
Purchase #7	$249.57	13.483%	$283.2195	$283.22	$283.20	$283.20
7 purchase totals =	$1,043.09		$1,132.2705	$1,132.27	$1,132.20	$1,132.30