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	$104.35	7.592%	$112.2723	$112.27	$112.25	$112.30
Purchase #2	$228.73	9.124%	$249.5993	$249.60	$249.60	$249.60
Purchase #3	$105.60	6.767%	$112.746	$112.75	$112.75	$112.70
Purchase #4	$35.39	10.495%	$39.1042	$39.10	$39.10	$39.10
Purchase #5	$24.56	5.474%	$25.9044	$25.90	$25.90	$25.90
Purchase #6	$152.61	10.483%	$168.6081	$168.61	$168.60	$168.60
Purchase #7	$137.77	9.564%	$150.9463	$150.95	$150.95	$150.90
7 purchase totals =	$789.01		$859.1806	$859.18	$859.15	$859.10