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	$38.80	10.576%	$42.9035	$42.90	$42.90	$42.90
Purchase #2	$205.98	6.823%	$220.034	$220.03	$220.05	$220.00
Purchase #3	$37.81	10.769%	$41.8818	$41.88	$41.90	$41.90
Purchase #4	$121.84	7.704%	$131.2266	$131.23	$131.25	$131.20
Purchase #5	$30.66	10.513%	$33.8833	$33.88	$33.90	$33.90
Purchase #6	$237.59	13.815%	$270.4131	$270.41	$270.40	$270.40
Purchase #7	$74.74	9.683%	$81.9771	$81.98	$82.00	$82.00
7 purchase totals =	$747.42		$822.3194	$822.31	$822.40	$822.30