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	$218.40	13.626%	$248.1592	$248.16	$248.15	$248.20
Purchase #2	$34.96	7.597%	$37.6159	$37.62	$37.60	$37.60
Purchase #3	$170.37	8.514%	$184.8753	$184.88	$184.90	$184.90
Purchase #4	$24.33	11.773%	$27.1944	$27.19	$27.20	$27.20
Purchase #5	$57.61	7.677%	$62.0327	$62.03	$62.05	$62.00
Purchase #6	$86.81	4.322%	$90.5619	$90.56	$90.55	$90.60
Purchase #7	$223.88	8.782%	$243.5411	$243.54	$243.55	$243.50
7 purchase totals =	$816.36		$893.9805	$893.98	$894.00	$894.00