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	$116.32	7.134%	$124.6183	$124.62	$124.60	$124.60
Purchase #2	$132.71	5.199%	$139.6096	$139.61	$139.60	$139.60
Purchase #3	$250.48	4.498%	$261.7466	$261.75	$261.75	$261.70
Purchase #4	$112.57	10.134%	$123.9778	$123.98	$124.00	$124.00
Purchase #5	$127.38	3.156%	$131.4001	$131.40	$131.40	$131.40
Purchase #6	$161.90	5.839%	$171.3533	$171.35	$171.35	$171.40
Purchase #7	$131.92	9.479%	$144.4247	$144.42	$144.40	$144.40
7 purchase totals =	$1,033.28		$1,097.1304	$1,097.13	$1,097.10	$1,097.10