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	$179.40	11.112%	$199.3349	$199.33	$199.35	$199.30
Purchase #2	$125.54	8.755%	$136.531	$136.53	$136.55	$136.50
Purchase #3	$246.66	13.717%	$280.4944	$280.49	$280.50	$280.50
Purchase #4	$29.37	12.584%	$33.0659	$33.07	$33.05	$33.10
Purchase #5	$177.56	12.419%	$199.6112	$199.61	$199.60	$199.60
Purchase #6	$82.74	8.420%	$89.7067	$89.71	$89.70	$89.70
Purchase #7	$80.42	11.666%	$89.8018	$89.80	$89.80	$89.80
7 purchase totals =	$921.69		$1,028.5459	$1,028.54	$1,028.55	$1,028.50