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	$107.41	9.106%	$117.1908	$117.19	$117.20	$117.20
Purchase #2	$222.76	6.342%	$236.8874	$236.89	$236.90	$236.90
Purchase #3	$195.66	13.839%	$222.7374	$222.74	$222.75	$222.70
Purchase #4	$29.45	6.816%	$31.4573	$31.46	$31.45	$31.50
Purchase #5	$104.81	4.336%	$109.3546	$109.35	$109.35	$109.40
Purchase #6	$109.55	7.180%	$117.4157	$117.42	$117.40	$117.40
Purchase #7	$50.50	5.196%	$53.124	$53.12	$53.10	$53.10
7 purchase totals =	$820.14		$888.1672	$888.17	$888.15	$888.20