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	$121.87	13.132%	$137.874	$137.87	$137.85	$137.90
Purchase #2	$6.85	10.834%	$7.5921	$7.59	$7.60	$7.60
Purchase #3	$179.85	6.657%	$191.8226	$191.82	$191.80	$191.80
Purchase #4	$35.72	11.609%	$39.8667	$39.87	$39.85	$39.90
Purchase #5	$244.98	9.458%	$268.1502	$268.15	$268.15	$268.20
Purchase #6	$85.94	6.152%	$91.227	$91.23	$91.25	$91.20
Purchase #7	$154.49	7.315%	$165.7909	$165.79	$165.80	$165.80
7 purchase totals =	$829.70		$902.3235	$902.32	$902.30	$902.40