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	$248.36	11.396%	$276.6631	$276.66	$276.65	$276.70
Purchase #2	$54.94	12.414%	$61.7603	$61.76	$61.75	$61.80
Purchase #3	$116.62	10.529%	$128.8989	$128.90	$128.90	$128.90
Purchase #4	$87.31	10.543%	$96.5151	$96.52	$96.50	$96.50
Purchase #5	$201.28	12.481%	$226.4018	$226.40	$226.40	$226.40
Purchase #6	$98.33	11.698%	$109.8326	$109.83	$109.85	$109.80
Purchase #7	$171.96	9.813%	$188.8344	$188.83	$188.85	$188.80
7 purchase totals =	$978.80		$1,088.9062	$1,088.90	$1,088.90	$1,088.90