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	$5.48	13.526%	$6.2212	$6.22	$6.20	$6.20
Purchase #2	$74.85	4.369%	$78.1202	$78.12	$78.10	$78.10
Purchase #3	$16.34	11.552%	$18.2276	$18.23	$18.25	$18.20
Purchase #4	$94.47	11.542%	$105.3737	$105.37	$105.35	$105.40
Purchase #5	$108.73	13.210%	$123.0932	$123.09	$123.10	$123.10
Purchase #6	$88.69	10.287%	$97.8135	$97.81	$97.80	$97.80
Purchase #7	$184.50	12.761%	$208.044	$208.04	$208.05	$208.00
7 purchase totals =	$573.06		$636.8934	$636.88	$636.85	$636.80