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	$54.75	5.463%	$57.741	$57.74	$57.75	$57.70
Purchase #2	$142.66	12.272%	$160.1672	$160.17	$160.15	$160.20
Purchase #3	$235.40	4.475%	$245.9342	$245.93	$245.95	$245.90
Purchase #4	$53.57	10.353%	$59.1161	$59.12	$59.10	$59.10
Purchase #5	$76.54	9.198%	$83.5801	$83.58	$83.60	$83.60
Purchase #6	$72.62	13.534%	$82.4484	$82.45	$82.45	$82.40
Purchase #7	$17.33	5.725%	$18.3221	$18.32	$18.30	$18.30
7 purchase totals =	$652.87		$707.3091	$707.31	$707.30	$707.20