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	$131.64	8.152%	$142.3713	$142.37	$142.35	$142.40
Purchase #2	$43.53	6.839%	$46.507	$46.51	$46.50	$46.50
Purchase #3	$28.41	11.874%	$31.7834	$31.78	$31.80	$31.80
Purchase #4	$228.36	13.805%	$259.8851	$259.89	$259.90	$259.90
Purchase #5	$157.59	13.429%	$178.7528	$178.75	$178.75	$178.80
Purchase #6	$71.57	9.628%	$78.4608	$78.46	$78.45	$78.50
Purchase #7	$218.77	12.479%	$246.0703	$246.07	$246.05	$246.10
7 purchase totals =	$879.87		$983.8307	$983.83	$983.80	$984.00