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	$66.48	4.368%	$69.3838	$69.38	$69.40	$69.40
Purchase #2	$174.69	5.274%	$183.9032	$183.90	$183.90	$183.90
Purchase #3	$54.71	8.553%	$59.3893	$59.39	$59.40	$59.40
Purchase #4	$243.32	12.288%	$273.2192	$273.22	$273.20	$273.20
Purchase #5	$125.42	13.411%	$142.2401	$142.24	$142.25	$142.20
Purchase #6	$155.81	13.496%	$176.8381	$176.84	$176.85	$176.80
Purchase #7	$165.87	6.625%	$176.8589	$176.86	$176.85	$176.90
7 purchase totals =	$986.30		$1,081.8326	$1,081.83	$1,081.85	$1,081.80