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	$79.75	11.710%	$89.0887	$89.09	$89.10	$89.10
Purchase #2	$218.39	6.712%	$233.0483	$233.05	$233.05	$233.00
Purchase #3	$133.31	6.105%	$141.4486	$141.45	$141.45	$141.40
Purchase #4	$199.54	4.723%	$208.9643	$208.96	$208.95	$209.00
Purchase #5	$172.91	13.772%	$196.7232	$196.72	$196.70	$196.70
Purchase #6	$201.65	8.787%	$219.369	$219.37	$219.35	$219.40
Purchase #7	$102.75	6.261%	$109.1832	$109.18	$109.20	$109.20
7 purchase totals =	$1,108.30		$1,197.8253	$1,197.82	$1,197.80	$1,197.80