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	$135.47	5.813%	$143.3449	$143.34	$143.35	$143.30
Purchase #2	$57.54	3.345%	$59.4647	$59.46	$59.45	$59.50
Purchase #3	$83.94	5.754%	$88.7699	$88.77	$88.75	$88.80
Purchase #4	$53.31	12.744%	$60.1038	$60.10	$60.10	$60.10
Purchase #5	$102.81	6.377%	$109.3662	$109.37	$109.35	$109.40
Purchase #6	$103.59	11.799%	$115.8126	$115.81	$115.80	$115.80
Purchase #7	$8.93	6.618%	$9.521	$9.52	$9.50	$9.50
7 purchase totals =	$545.59		$586.3831	$586.37	$586.30	$586.40