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	$30.78	10.187%	$33.9156	$33.92	$33.90	$33.90
Purchase #2	$168.58	7.209%	$180.7329	$180.73	$180.75	$180.70
Purchase #3	$181.33	9.656%	$198.8392	$198.84	$198.85	$198.80
Purchase #4	$38.88	10.326%	$42.8947	$42.89	$42.90	$42.90
Purchase #5	$232.82	3.443%	$240.836	$240.84	$240.85	$240.80
Purchase #6	$127.64	7.344%	$137.0139	$137.01	$137.00	$137.00
Purchase #7	$28.30	11.621%	$31.5887	$31.59	$31.60	$31.60
7 purchase totals =	$808.33		$865.8210	$865.82	$865.85	$865.70