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	$40.78	3.584%	$42.2416	$42.24	$42.25	$42.20
Purchase #2	$206.84	10.195%	$227.9273	$227.93	$227.95	$227.90
Purchase #3	$156.97	7.292%	$168.4163	$168.42	$168.40	$168.40
Purchase #4	$250.63	3.341%	$259.0035	$259.00	$259.00	$259.00
Purchase #5	$104.60	9.834%	$114.8864	$114.89	$114.90	$114.90
Purchase #6	$99.80	4.585%	$104.3758	$104.38	$104.40	$104.40
Purchase #7	$53.86	10.551%	$59.5428	$59.54	$59.55	$59.50
7 purchase totals =	$913.48		$976.3937	$976.40	$976.45	$976.30