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	$248.63	8.839%	$270.6064	$270.61	$270.60	$270.60
Purchase #2	$111.63	3.271%	$115.2814	$115.28	$115.30	$115.30
Purchase #3	$117.86	9.166%	$128.663	$128.66	$128.65	$128.70
Purchase #4	$166.83	12.216%	$187.21	$187.21	$187.20	$187.20
Purchase #5	$227.93	12.700%	$256.8771	$256.88	$256.90	$256.90
Purchase #6	$131.33	12.319%	$147.5085	$147.51	$147.50	$147.50
Purchase #7	$37.48	12.480%	$42.1575	$42.16	$42.15	$42.20
7 purchase totals =	$1,041.69		$1,148.3039	$1,148.31	$1,148.30	$1,148.40