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	$37.30	4.640%	$39.0307	$39.03	$39.05	$39.00
Purchase #2	$153.83	7.844%	$165.8964	$165.90	$165.90	$165.90
Purchase #3	$245.82	9.566%	$269.3351	$269.34	$269.35	$269.30
Purchase #4	$16.34	13.860%	$18.6047	$18.60	$18.60	$18.60
Purchase #5	$231.48	11.691%	$258.5423	$258.54	$258.55	$258.50
Purchase #6	$112.47	12.203%	$126.1947	$126.19	$126.20	$126.20
Purchase #7	$227.81	11.471%	$253.9421	$253.94	$253.95	$253.90
7 purchase totals =	$1,025.05		$1,131.5460	$1,131.54	$1,131.60	$1,131.40