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	$220.90	3.457%	$228.5365	$228.54	$228.55	$228.50
Purchase #2	$33.90	11.185%	$37.6917	$37.69	$37.70	$37.70
Purchase #3	$79.56	13.453%	$90.2632	$90.26	$90.25	$90.30
Purchase #4	$24.47	13.731%	$27.83	$27.83	$27.85	$27.80
Purchase #5	$164.29	3.103%	$169.3879	$169.39	$169.40	$169.40
Purchase #6	$219.83	7.262%	$235.7941	$235.79	$235.80	$235.80
Purchase #7	$17.74	4.108%	$18.4688	$18.47	$18.45	$18.50
7 purchase totals =	$760.69		$807.9722	$807.97	$808.00	$808.00