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	$237.88	7.131%	$254.8432	$254.84	$254.85	$254.80
Purchase #2	$167.67	7.835%	$180.8069	$180.81	$180.80	$180.80
Purchase #3	$180.87	5.800%	$191.3605	$191.36	$191.35	$191.40
Purchase #4	$249.56	12.255%	$280.1436	$280.14	$280.15	$280.10
Purchase #5	$94.97	11.179%	$105.5867	$105.59	$105.60	$105.60
Purchase #6	$112.28	11.787%	$125.5144	$125.51	$125.50	$125.50
Purchase #7	$160.55	13.286%	$181.8807	$181.88	$181.90	$181.90
7 purchase totals =	$1,203.78		$1,320.1360	$1,320.13	$1,320.15	$1,320.10