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	$191.47	11.479%	$213.4488	$213.45	$213.45	$213.40
Purchase #2	$126.86	10.562%	$140.259	$140.26	$140.25	$140.30
Purchase #3	$13.88	6.280%	$14.7517	$14.75	$14.75	$14.80
Purchase #4	$40.67	6.270%	$43.22	$43.22	$43.20	$43.20
Purchase #5	$138.59	7.272%	$148.6683	$148.67	$148.65	$148.70
Purchase #6	$130.91	13.688%	$148.829	$148.83	$148.85	$148.80
Purchase #7	$105.73	5.703%	$111.7598	$111.76	$111.75	$111.80
7 purchase totals =	$748.11		$820.9366	$820.94	$820.90	$821.00