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	$6.84	8.389%	$7.4138	$7.41	$7.40	$7.40
Purchase #2	$232.86	4.522%	$243.3899	$243.39	$243.40	$243.40
Purchase #3	$128.58	11.595%	$143.4889	$143.49	$143.50	$143.50
Purchase #4	$128.29	9.262%	$140.1722	$140.17	$140.15	$140.20
Purchase #5	$117.58	11.646%	$131.2734	$131.27	$131.25	$131.30
Purchase #6	$211.63	3.113%	$218.218	$218.22	$218.20	$218.20
Purchase #7	$131.97	3.813%	$137.002	$137.00	$137.00	$137.00
7 purchase totals =	$957.75		$1,020.9582	$1,020.95	$1,020.90	$1,021.00