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	$178.82	11.168%	$198.7906	$198.79	$198.80	$198.80
Purchase #2	$174.60	9.495%	$191.1783	$191.18	$191.20	$191.20
Purchase #3	$136.45	6.712%	$145.6085	$145.61	$145.60	$145.60
Purchase #4	$241.37	11.580%	$269.3206	$269.32	$269.30	$269.30
Purchase #5	$67.54	8.459%	$73.2532	$73.25	$73.25	$73.30
Purchase #6	$119.31	3.844%	$123.8963	$123.90	$123.90	$123.90
Purchase #7	$33.30	8.338%	$36.0766	$36.08	$36.10	$36.10
7 purchase totals =	$951.39		$1,038.1241	$1,038.13	$1,038.15	$1,038.20