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	$233.73	4.269%	$243.7079	$243.71	$243.70	$243.70
Purchase #2	$184.90	3.606%	$191.5675	$191.57	$191.55	$191.60
Purchase #3	$124.63	5.791%	$131.8473	$131.85	$131.85	$131.80
Purchase #4	$24.76	11.288%	$27.5549	$27.55	$27.55	$27.60
Purchase #5	$154.91	8.784%	$168.5173	$168.52	$168.50	$168.50
Purchase #6	$147.78	7.559%	$158.9507	$158.95	$158.95	$159.00
Purchase #7	$43.54	5.189%	$45.7993	$45.80	$45.80	$45.80
7 purchase totals =	$914.25		$967.9449	$967.95	$967.90	$968.00