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	$95.96	7.466%	$103.1244	$103.12	$103.10	$103.10
Purchase #2	$229.92	6.767%	$245.4787	$245.48	$245.50	$245.50
Purchase #3	$53.73	11.285%	$59.7934	$59.79	$59.80	$59.80
Purchase #4	$45.51	12.482%	$51.1906	$51.19	$51.20	$51.20
Purchase #5	$239.34	9.818%	$262.8384	$262.84	$262.85	$262.80
Purchase #6	$129.56	9.258%	$141.5547	$141.55	$141.55	$141.60
Purchase #7	$122.73	3.145%	$126.5899	$126.59	$126.60	$126.60
7 purchase totals =	$916.75		$990.5701	$990.56	$990.60	$990.60