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	$75.45	6.816%	$80.5927	$80.59	$80.60	$80.60
Purchase #2	$31.31	5.681%	$33.0887	$33.09	$33.10	$33.10
Purchase #3	$112.25	7.609%	$120.7911	$120.79	$120.80	$120.80
Purchase #4	$104.39	13.520%	$118.5035	$118.50	$118.50	$118.50
Purchase #5	$192.56	13.334%	$218.236	$218.24	$218.25	$218.20
Purchase #6	$250.41	12.577%	$281.9041	$281.90	$281.90	$281.90
Purchase #7	$157.91	13.491%	$179.2136	$179.21	$179.20	$179.20
7 purchase totals =	$924.28		$1,032.3297	$1,032.32	$1,032.35	$1,032.30