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	$96.55	13.711%	$109.788	$109.79	$109.80	$109.80
Purchase #2	$122.90	3.534%	$127.2433	$127.24	$127.25	$127.20
Purchase #3	$179.76	8.217%	$194.5309	$194.53	$194.55	$194.50
Purchase #4	$180.79	10.527%	$199.8218	$199.82	$199.80	$199.80
Purchase #5	$42.71	12.142%	$47.8958	$47.90	$47.90	$47.90
Purchase #6	$103.39	11.379%	$115.1547	$115.15	$115.15	$115.20
Purchase #7	$58.94	11.201%	$65.5419	$65.54	$65.55	$65.50
7 purchase totals =	$785.04		$859.9764	$859.97	$860.00	$859.90