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	$131.26	9.624%	$143.8925	$143.89	$143.90	$143.90
Purchase #2	$220.68	7.347%	$236.8934	$236.89	$236.90	$236.90
Purchase #3	$214.82	9.476%	$235.1763	$235.18	$235.20	$235.20
Purchase #4	$141.48	10.461%	$156.2802	$156.28	$156.30	$156.30
Purchase #5	$145.43	3.645%	$150.7309	$150.73	$150.75	$150.70
Purchase #6	$188.73	13.134%	$213.5178	$213.52	$213.50	$213.50
Purchase #7	$73.71	12.520%	$82.9385	$82.94	$82.95	$82.90
7 purchase totals =	$1,116.11		$1,219.4296	$1,219.43	$1,219.50	$1,219.40