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	$152.73	6.657%	$162.8972	$162.90	$162.90	$162.90
Purchase #2	$198.58	13.419%	$225.2275	$225.23	$225.25	$225.20
Purchase #3	$225.97	6.751%	$241.2252	$241.23	$241.25	$241.20
Purchase #4	$66.38	10.860%	$73.5889	$73.59	$73.60	$73.60
Purchase #5	$200.34	5.458%	$211.2746	$211.27	$211.25	$211.30
Purchase #6	$154.25	7.577%	$165.9375	$165.94	$165.95	$165.90
Purchase #7	$184.32	13.450%	$209.111	$209.11	$209.10	$209.10
7 purchase totals =	$1,182.57		$1,289.2619	$1,289.27	$1,289.30	$1,289.20