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	$229.93	12.296%	$258.2022	$258.20	$258.20	$258.20
Purchase #2	$35.58	9.694%	$39.0291	$39.03	$39.05	$39.00
Purchase #3	$49.78	11.677%	$55.5928	$55.59	$55.60	$55.60
Purchase #4	$79.53	13.229%	$90.051	$90.05	$90.05	$90.10
Purchase #5	$180.80	13.473%	$205.1592	$205.16	$205.15	$205.20
Purchase #6	$213.91	4.267%	$223.0375	$223.04	$223.05	$223.00
Purchase #7	$180.29	7.315%	$193.4782	$193.48	$193.50	$193.50
7 purchase totals =	$969.82		$1,064.5500	$1,064.55	$1,064.60	$1,064.60