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	$149.60	3.539%	$154.8943	$154.89	$154.90	$154.90
Purchase #2	$145.56	11.787%	$162.7172	$162.72	$162.70	$162.70
Purchase #3	$201.72	12.569%	$227.0742	$227.07	$227.05	$227.10
Purchase #4	$189.95	4.309%	$198.1349	$198.13	$198.15	$198.10
Purchase #5	$116.59	11.783%	$130.3278	$130.33	$130.35	$130.30
Purchase #6	$159.75	6.138%	$169.5555	$169.56	$169.55	$169.60
Purchase #7	$80.25	11.811%	$89.7283	$89.73	$89.75	$89.70
7 purchase totals =	$1,043.42		$1,132.4322	$1,132.43	$1,132.45	$1,132.40