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	$12.97	5.583%	$13.6941	$13.69	$13.70	$13.70
Purchase #2	$64.92	7.229%	$69.6131	$69.61	$69.60	$69.60
Purchase #3	$117.96	9.238%	$128.8571	$128.86	$128.85	$128.90
Purchase #4	$40.93	5.266%	$43.0854	$43.09	$43.10	$43.10
Purchase #5	$77.28	6.360%	$82.195	$82.20	$82.20	$82.20
Purchase #6	$70.69	13.143%	$79.9808	$79.98	$80.00	$80.00
Purchase #7	$165.76	9.122%	$180.8806	$180.88	$180.90	$180.90
7 purchase totals =	$550.51		$598.3061	$598.31	$598.35	$598.40