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	$128.79	5.841%	$136.3126	$136.31	$136.30	$136.30
Purchase #2	$117.32	5.289%	$123.5251	$123.53	$123.55	$123.50
Purchase #3	$71.88	12.871%	$81.1317	$81.13	$81.15	$81.10
Purchase #4	$51.40	7.279%	$55.1414	$55.14	$55.15	$55.10
Purchase #5	$175.39	4.518%	$183.3141	$183.31	$183.30	$183.30
Purchase #6	$145.92	9.642%	$159.9896	$159.99	$160.00	$160.00
Purchase #7	$29.78	12.364%	$33.462	$33.46	$33.45	$33.50
7 purchase totals =	$720.48		$772.8765	$772.87	$772.90	$772.80