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	$172.92	9.306%	$189.0119	$189.01	$189.00	$189.00
Purchase #2	$234.36	3.767%	$243.1883	$243.19	$243.20	$243.20
Purchase #3	$248.90	10.604%	$275.2934	$275.29	$275.30	$275.30
Purchase #4	$134.35	4.246%	$140.0545	$140.05	$140.05	$140.10
Purchase #5	$69.97	3.747%	$72.5918	$72.59	$72.60	$72.60
Purchase #6	$184.50	6.494%	$196.4814	$196.48	$196.50	$196.50
Purchase #7	$37.73	11.552%	$42.0886	$42.09	$42.10	$42.10
7 purchase totals =	$1,082.73		$1,158.7099	$1,158.70	$1,158.75	$1,158.80