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	$73.75	3.724%	$76.4965	$76.50	$76.50	$76.50
Purchase #2	$88.83	6.765%	$94.8393	$94.84	$94.85	$94.80
Purchase #3	$155.56	11.818%	$173.9441	$173.94	$173.95	$173.90
Purchase #4	$16.63	9.704%	$18.2438	$18.24	$18.25	$18.20
Purchase #5	$6.84	7.768%	$7.3713	$7.37	$7.35	$7.40
Purchase #6	$35.88	13.806%	$40.8336	$40.83	$40.85	$40.80
Purchase #7	$219.86	10.574%	$243.108	$243.11	$243.10	$243.10
7 purchase totals =	$597.35		$654.8366	$654.83	$654.85	$654.70