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	$72.63	13.347%	$82.3239	$82.32	$82.30	$82.30
Purchase #2	$176.67	11.416%	$196.8386	$196.84	$196.85	$196.80
Purchase #3	$47.83	7.154%	$51.2518	$51.25	$51.25	$51.30
Purchase #4	$73.82	8.637%	$80.1958	$80.20	$80.20	$80.20
Purchase #5	$142.51	3.301%	$147.2143	$147.21	$147.20	$147.20
Purchase #6	$177.88	12.689%	$200.4512	$200.45	$200.45	$200.50
Purchase #7	$60.55	11.653%	$67.6059	$67.61	$67.60	$67.60
7 purchase totals =	$751.89		$825.8815	$825.88	$825.85	$825.90