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	$249.38	4.264%	$260.0136	$260.01	$260.00	$260.00
Purchase #2	$27.69	13.103%	$31.3182	$31.32	$31.30	$31.30
Purchase #3	$137.86	9.410%	$150.8326	$150.83	$150.85	$150.80
Purchase #4	$69.57	9.673%	$76.2995	$76.30	$76.30	$76.30
Purchase #5	$153.90	3.251%	$158.9033	$158.90	$158.90	$158.90
Purchase #6	$36.96	9.187%	$40.3555	$40.36	$40.35	$40.40
Purchase #7	$242.83	8.644%	$263.8202	$263.82	$263.80	$263.80
7 purchase totals =	$918.19		$981.5429	$981.54	$981.50	$981.50