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	$220.53	12.846%	$248.8593	$248.86	$248.85	$248.90
Purchase #2	$122.62	6.860%	$131.0317	$131.03	$131.05	$131.00
Purchase #3	$125.72	4.254%	$131.0681	$131.07	$131.05	$131.10
Purchase #4	$115.49	10.842%	$128.0114	$128.01	$128.00	$128.00
Purchase #5	$238.60	6.714%	$254.6196	$254.62	$254.60	$254.60
Purchase #6	$195.51	7.111%	$209.4127	$209.41	$209.40	$209.40
Purchase #7	$25.54	9.296%	$27.9142	$27.91	$27.90	$27.90
7 purchase totals =	$1,044.01		$1,130.9170	$1,130.91	$1,130.85	$1,130.90