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	$172.94	5.493%	$182.4396	$182.44	$182.45	$182.40
Purchase #2	$212.46	4.524%	$222.0717	$222.07	$222.05	$222.10
Purchase #3	$201.82	9.304%	$220.5973	$220.60	$220.60	$220.60
Purchase #4	$244.82	12.459%	$275.3221	$275.32	$275.30	$275.30
Purchase #5	$52.91	12.322%	$59.4296	$59.43	$59.45	$59.40
Purchase #6	$112.78	13.487%	$127.9906	$127.99	$128.00	$128.00
Purchase #7	$130.62	7.499%	$140.4152	$140.42	$140.40	$140.40
7 purchase totals =	$1,128.35		$1,228.2661	$1,228.27	$1,228.25	$1,228.20