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	$81.52	10.839%	$90.356	$90.36	$90.35	$90.40
Purchase #2	$91.88	3.756%	$95.331	$95.33	$95.35	$95.30
Purchase #3	$250.53	12.805%	$282.6104	$282.61	$282.60	$282.60
Purchase #4	$60.36	3.760%	$62.6295	$62.63	$62.65	$62.60
Purchase #5	$31.47	5.842%	$33.3085	$33.31	$33.30	$33.30
Purchase #6	$81.80	12.777%	$92.2516	$92.25	$92.25	$92.30
Purchase #7	$163.73	4.535%	$171.1552	$171.16	$171.15	$171.20
7 purchase totals =	$761.29		$827.6422	$827.65	$827.65	$827.70