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	$238.63	5.122%	$250.8526	$250.85	$250.85	$250.90
Purchase #2	$85.32	7.216%	$91.4767	$91.48	$91.50	$91.50
Purchase #3	$131.33	9.213%	$143.4294	$143.43	$143.45	$143.40
Purchase #4	$116.31	5.348%	$122.5303	$122.53	$122.55	$122.50
Purchase #5	$161.62	9.132%	$176.3791	$176.38	$176.40	$176.40
Purchase #6	$34.89	6.592%	$37.1899	$37.19	$37.20	$37.20
Purchase #7	$42.30	3.677%	$43.8554	$43.86	$43.85	$43.90
7 purchase totals =	$810.40		$865.7134	$865.72	$865.80	$865.80