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	$31.58	4.157%	$32.8928	$32.89	$32.90	$32.90
Purchase #2	$209.96	9.128%	$229.1251	$229.13	$229.15	$229.10
Purchase #3	$107.52	3.490%	$111.2724	$111.27	$111.25	$111.30
Purchase #4	$36.50	6.296%	$38.798	$38.80	$38.80	$38.80
Purchase #5	$235.45	11.844%	$263.3367	$263.34	$263.35	$263.30
Purchase #6	$168.53	8.815%	$183.3859	$183.39	$183.40	$183.40
Purchase #7	$23.47	8.808%	$25.5372	$25.54	$25.55	$25.50
7 purchase totals =	$813.01		$884.3481	$884.36	$884.40	$884.30