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	$25.79	4.863%	$27.0442	$27.04	$27.05	$27.00
Purchase #2	$116.53	11.372%	$129.7818	$129.78	$129.80	$129.80
Purchase #3	$199.71	9.857%	$219.3954	$219.40	$219.40	$219.40
Purchase #4	$149.66	12.167%	$167.8691	$167.87	$167.85	$167.90
Purchase #5	$29.39	10.684%	$32.53	$32.53	$32.55	$32.50
Purchase #6	$52.34	13.577%	$59.4462	$59.45	$59.45	$59.40
Purchase #7	$142.36	4.601%	$148.91	$148.91	$148.90	$148.90
7 purchase totals =	$715.78		$784.9767	$784.98	$785.00	$784.90