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	$75.42	4.590%	$78.8818	$78.88	$78.90	$78.90
Purchase #2	$221.77	12.243%	$248.9213	$248.92	$248.90	$248.90
Purchase #3	$48.54	13.514%	$55.0997	$55.10	$55.10	$55.10
Purchase #4	$169.56	7.540%	$182.3448	$182.34	$182.35	$182.30
Purchase #5	$169.35	4.822%	$177.5161	$177.52	$177.50	$177.50
Purchase #6	$160.79	10.186%	$177.1681	$177.17	$177.15	$177.20
Purchase #7	$38.88	4.139%	$40.4892	$40.49	$40.50	$40.50
7 purchase totals =	$884.31		$960.4210	$960.42	$960.40	$960.40