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	$6.40	7.544%	$6.8828	$6.88	$6.90	$6.90
Purchase #2	$150.79	6.197%	$160.1345	$160.13	$160.15	$160.10
Purchase #3	$148.40	9.425%	$162.3867	$162.39	$162.40	$162.40
Purchase #4	$155.46	9.732%	$170.5894	$170.59	$170.60	$170.60
Purchase #5	$116.83	12.428%	$131.3496	$131.35	$131.35	$131.30
Purchase #6	$176.79	13.204%	$200.1334	$200.13	$200.15	$200.10
Purchase #7	$178.98	8.298%	$193.8318	$193.83	$193.85	$193.80
7 purchase totals =	$933.65		$1,025.3082	$1,025.30	$1,025.40	$1,025.20