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	$161.41	4.340%	$168.4152	$168.42	$168.40	$168.40
Purchase #2	$130.87	7.779%	$141.0504	$141.05	$141.05	$141.10
Purchase #3	$42.66	6.471%	$45.4205	$45.42	$45.40	$45.40
Purchase #4	$196.81	12.221%	$220.8622	$220.86	$220.85	$220.90
Purchase #5	$245.93	13.555%	$279.2658	$279.27	$279.25	$279.30
Purchase #6	$203.59	8.417%	$220.7262	$220.73	$220.75	$220.70
Purchase #7	$48.97	5.282%	$51.5566	$51.56	$51.55	$51.60
7 purchase totals =	$1,030.24		$1,127.2969	$1,127.31	$1,127.25	$1,127.40