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	$46.66	4.152%	$48.5973	$48.60	$48.60	$48.60
Purchase #2	$220.39	6.816%	$235.4118	$235.41	$235.40	$235.40
Purchase #3	$98.77	10.580%	$109.2199	$109.22	$109.20	$109.20
Purchase #4	$239.77	10.681%	$265.3798	$265.38	$265.40	$265.40
Purchase #5	$38.89	8.465%	$42.182	$42.18	$42.20	$42.20
Purchase #6	$205.61	9.372%	$224.8798	$224.88	$224.90	$224.90
Purchase #7	$246.28	11.738%	$275.1883	$275.19	$275.20	$275.20
7 purchase totals =	$1,096.37		$1,200.8589	$1,200.86	$1,200.90	$1,200.90