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	$7.42	6.549%	$7.9059	$7.91	$7.90	$7.90
Purchase #2	$111.46	13.492%	$126.4982	$126.50	$126.50	$126.50
Purchase #3	$136.76	13.726%	$155.5317	$155.53	$155.55	$155.50
Purchase #4	$181.31	13.169%	$205.1867	$205.19	$205.20	$205.20
Purchase #5	$100.36	13.207%	$113.6145	$113.61	$113.60	$113.60
Purchase #6	$82.37	11.470%	$91.8178	$91.82	$91.80	$91.80
Purchase #7	$188.40	13.192%	$213.2537	$213.25	$213.25	$213.30
7 purchase totals =	$808.08		$913.8085	$913.81	$913.80	$913.80