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	$122.60	13.697%	$139.3925	$139.39	$139.40	$139.40
Purchase #2	$81.79	9.779%	$89.7882	$89.79	$89.80	$89.80
Purchase #3	$53.93	3.398%	$55.7625	$55.76	$55.75	$55.80
Purchase #4	$124.73	12.593%	$140.4372	$140.44	$140.45	$140.40
Purchase #5	$27.72	3.519%	$28.6955	$28.70	$28.70	$28.70
Purchase #6	$189.78	8.799%	$206.4787	$206.48	$206.50	$206.50
Purchase #7	$44.45	6.429%	$47.3077	$47.31	$47.30	$47.30
7 purchase totals =	$645.00		$707.8623	$707.87	$707.90	$707.90