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	$249.89	9.263%	$273.0373	$273.04	$273.05	$273.00
Purchase #2	$43.68	7.121%	$46.7905	$46.79	$46.80	$46.80
Purchase #3	$81.46	10.281%	$89.8349	$89.83	$89.85	$89.80
Purchase #4	$245.49	6.612%	$261.7218	$261.72	$261.70	$261.70
Purchase #5	$31.78	7.483%	$34.1581	$34.16	$34.15	$34.20
Purchase #6	$105.39	11.800%	$117.826	$117.83	$117.85	$117.80
Purchase #7	$156.37	13.741%	$177.8568	$177.86	$177.85	$177.90
7 purchase totals =	$914.06		$1,001.2254	$1,001.23	$1,001.25	$1,001.20