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	$35.82	9.667%	$39.2827	$39.28	$39.30	$39.30
Purchase #2	$90.36	7.534%	$97.1677	$97.17	$97.15	$97.20
Purchase #3	$13.31	4.466%	$13.9044	$13.90	$13.90	$13.90
Purchase #4	$101.61	9.801%	$111.5688	$111.57	$111.55	$111.60
Purchase #5	$13.50	3.727%	$14.0031	$14.00	$14.00	$14.00
Purchase #6	$53.56	8.696%	$58.2176	$58.22	$58.20	$58.20
Purchase #7	$51.64	5.133%	$54.2907	$54.29	$54.30	$54.30
7 purchase totals =	$359.80		$388.4350	$388.43	$388.40	$388.50