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	$127.27	3.224%	$131.3732	$131.37	$131.35	$131.40
Purchase #2	$183.80	5.810%	$194.4788	$194.48	$194.50	$194.50
Purchase #3	$164.39	7.380%	$176.522	$176.52	$176.50	$176.50
Purchase #4	$91.98	13.866%	$104.7339	$104.73	$104.75	$104.70
Purchase #5	$179.60	9.574%	$196.7949	$196.79	$196.80	$196.80
Purchase #6	$55.92	9.111%	$61.0149	$61.01	$61.00	$61.00
Purchase #7	$83.48	12.574%	$93.9768	$93.98	$94.00	$94.00
7 purchase totals =	$886.44		$958.8945	$958.88	$958.90	$958.90